Uterine leiomyoma is associated with the risk of developing endometriosis: A nationwide cohort study involving 156,195 women.

OBJECTIVE: Evidence for an association between uterine leiomyoma and increased risk of endometriosis is limited by small sample sizes and short follow-up periods. We assessed this association in a large nationwide sample with 14 years of data.
DESIGN: Data were sourced from Taiwan's Longitudinal Health Insurance Database 2000 (LHID2000).
MATERIALS AND METHODS: We identified 31,239 women aged ≥20 years diagnosed with uterine leiomyoma (International Classification of Disease, Ninth Revision, Clinical Modification [ICD-9-CM] code 218) between Jan 1, 2000 and Dec 31, 2012, who were matched with 124,956 controls (1:4) by 5-year age groups and year of diagnosis. Follow-up was from the date of LHID2000 entry to the first occurrence of endometriosis, loss to follow-up, insurance termination, or until December 31, 2013, whichever was earlier.
RESULTS: In Cox regression analysis, the adjusted hazard ratio (aHR) for endometriosis in women with uterine leiomyoma was 6.44 (95% CI, 6.18, 6.72) compared with controls. The risk of endometriosis was significantly increased in women with uterine leiomyoma and comorbidities of tube-ovarian infection (aHR 2.86; 95% CI, 1.28, 6.36), endometritis (1.14; 1.06, 1.24), infertility (1.26; 1.16, 1.37), or allergic diseases (1.11; 1.05, 1.17). Having both uterine leiomyoma and endometritis significantly increased the risk of endometriosis (aHR 6.73; 95% CI, 6.07, 7.45) versus having only uterine leiomyoma (6.61; 6.33, 6.91) or endometritis (1.49; 1.31, 1.69). Similarly, having both uterine leiomyoma and infertility significantly increased the risk of endometriosis (aHR 6.95; 95% CI, 6.21, 7.78) versus having only uterine leiomyoma (6.66; 6.38, 6.96) or infertility (1.78; 1.57, 2.02).
CONCLUSIONS: A diagnosis of uterine leiomyoma appears to increase the risk of endometriosis. Patients presenting with uterine fibroids should be encouraged to give informed consent for possible simultaneous surgical treatment of endometriosis.

Introduction

Of all solid pelvic tumors, uterine leiomyoma is the most common, affecting as many as 80% of women [1, 2]. While many patients are asymptomatic, leiomyoma-related symptoms commonly include abnormal uterine bleeding, pressure-related bladder or bowel symptoms, pelvic pain, or reproductive dysfunction that may require medical or surgical intervention [1-5]. The pathogenesis of uterine leiomyoma is uncertain, but is likely to involve genetic predisposition, steroidal hormones and growth factors [5, 6]. Endometriosis is another common gynecological condition, affecting 10–50% of reproductive-aged women [7-9]. The most common symptoms are dysmenorrhea, chronic pelvic pain, dyspareunia and subfertility [10-12]. These symptoms can have enormous impact on a sufferer’s quality of life, with well-documented evidence describing how these symptoms interfere with daily life and activities, adversely affecting general health and psychological well-being, and impacting on overall sexual functioning [13-15]. Moreover, endometriosis-related symptoms impose a substantial economic burden on those afflicted in terms of direct costs of medical care and indirect costs, such as costs for sick leave and work absenteeism [14, 16]. It is well known that the risk of endometriosis is higher in young women with menstrual dysfunction and any obstruction to the outflow of menstrual products [17, 18]. This is thought to be because of the higher volume of refluxed menstrual blood and endometrial tissue fragments, lending support to the theory that endometriosis results from retrograde menstruation [17]. Genetic insights, the possible roles of the environment and the immune system, as well as intrinsic abnormalities in the endometrium of affected women have helped to elucidate the pathogenesis of endometriosis [19]. Endometriosis is an estrogen-dependent disorder. Recent speculations suggest that the estrogen-dependent activity of different ion channels may contribute to the etiology of endometriosis [20]. The levels of estrogen expression and functionality of these ion channels fluctuate between menstrual phases, with increased estrogen enhancing pathogenic aspects of endometriosis, such as the proliferation and in vivo implantation of ectopic endometrium [20]. More evidence is needed to determine the strength of this association. Available conventional therapeutic strategies for managing endometriosis (surgery, hormonal treatment, nonsteroidal anti-inflammatories) have limited or intermittent efficacy, as well as unwanted hormonal side effects such as the loss of bone density [21]. Aromatase inhibitors (AIs) have been proposed for endometriosis treatment, with limited clinical data indicating associated reductions in volume and symptoms of endometrioma, but AIs have also been linked to the development of functional cysts and menopausal symptoms, as well as reductions in bone mineral density [22]. Alternative progestins and estroprogestins drug delivery methods (e.g., vaginal rings, patches, subcutaneous implants, intrauterine drug delivery systems, nanotechnologies) offer potential advantages of fewer adverse events, greater therapeutic efficacy, improved patient compliance and satisfaction [23]. At this point, more clinical experience is needed before any conclusions can be made about the clinical efficacies of these alternative drug delivery methods [23]. Thus, the disadvantages of current pharmacotherapeutic options have induced many women with endometriosis to seek alternative treatment options, such as phytotherapy [21, 24]. Promisingly, in vitro and preclinical investigations have indicated that some phytochemicals demonstrate strong phytoestrogenic effects capable of modulating estrogen and inflammatory activity, which could help to reduce endometriosis symptoms, although randomized controlled trial data are lacking [21, 24]. Interestingly, increasing clinical and pathophysiological evidence supports the notion that chronic inflammation is associated with benign gynecological disorders such as uterine leiomyoma and endometriosis [25]. These associations have been comprehensively reviewed [25], although basic and clinical investigations have yet to clearly define the mechanism responsible for the development of endometriosis. Up until now, research has focused on altered immune responses and other regulatory factors that may mediate the histogenesis of endometriosis.

Uterine leiomyoma and endometriosis are hormone-dependent conditions that share many common clinical features including pelvic pain, menstrual abnormalities and subfertility. However, whether these disorders co-exist by chance or because they share common etiological factors is uncertain, as few studies have investigated the association. One research group from Finland has suggested that symptomatic endometriosis appears to coincide with symptomatic uterine fibroids [26]. In one study involving 3,684 Italian women with various gynecological conditions requiring surgery, 1,880 were diagnosed with fibroids and 219 (12%) of them had endometriosis [27], while in a Thai study in which 331 women underwent surgery for benign gynecological diseases, a high proportion (28%) had co-existing endometriosis and uterine leiomyoma [28]. The proportion was much higher among 208 US women who underwent surgery for symptomatic leiomyoma between March 2011 and December 2015 at a single tertiary medical center, where 181 (87.1%) were found to have endometriosis [29]. All of these studies are limited by their small sample sizes or relatively short follow-up periods. The existing literature contains no large studies with long-term follow-up that have investigated the association between leiomyoma, endometriosis and other comorbidities, such as tube-ovarian infection, endometritis, infertility, autoimmune diseases, allergic diseases, breast cancer, cervical cancer, and ovarian cancer.

The purpose of our study was to investigate the co-existence of endometriosis and leiomyoma using long-term data from Taiwan’s National Health Insurance Research Database (NHIRD). We specifically sought to determine whether having uterine leiomyoma increases the risk of developing endometriosis. We also examined the association between leiomyoma, endometriosis and other comorbidities in a large population from the same database.

Materials and methods

Data source

Taiwan’s National Health Insurance (NHI) Program provides universal health insurance and covers almost all residents nationwide. Our data source comprised the Longitudinal Health Insurance Database 2000 (LHID2000), a representative subset of 1,000,000 randomly selected enrollees from the Registry for 23 million beneficiaries of the NHI program. The personal identification numbers in the claims data were recorded in electronic format before their release for research, to ensure that the privacy was protected for all the insured individuals. As the data used in this study were completely anonymized and de-identified before access and analysis, there was no need to obtain informed patient consent. This study was approved by the Institutional Review Board of China Medical University Hospital in Taichung, Taiwan (CMUH104-REC2-115). Clinical diagnoses were classified based on the International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) codes.

Study participants

The case cohort consisted of women aged ≥20 years with a diagnosis of uterine leiomyoma (ICD-9-CM code 218) recorded in the LHID2000 between Jan 1, 2000 and Dec 31, 2012. The first recorded diagnosis of uterine leiomyoma served as the index date. Patients who had endometriosis before the index date or were aged less than 20 years were excluded. Controls were randomly selected from LHID2000 beneficiaries who did not have a recorded diagnosis of uterine leiomyoma and were frequency-matched (1:4) with cases within 5-year age groups and by the year of diagnosis. The detailed flowchart is presented in Fig 1.

Fig 1

Flowchart of study participants identified from the Longitudinal Health Insurance Database 2000 (LHID2000), a subset of Taiwan’s National Health Insurance Research Database (NHIRD).

The endpoint was a new diagnosis of endometriosis (ICD-9-CM code 617), which was defined as the first inpatient or outpatient date. The diagnosis of endometriosis was made by gynecologists when they identified endometriotic lesions during laparoscopy or ultrasound. All study participants were followed-up to the first occurrence of endometriosis, loss to follow-up, termination of NHI insurance, or until Dec 31, 2013, whichever was sooner.

Study participants were divided into three age groups: 20–39, 40–49, or ≥50 years. Several comorbidities were considered as potential confounders in this study, including tube-ovarian infection (ICD-9-CM code 614.2), endometritis (ICD-9-CM code 615), infertility (ICD-9-CM code 628), autoimmune diseases (ICD-9-CM code 710), allergic diseases (ICD-9-CM code 477, allergic rhinitis, which includes allergic rhinitis due to pollen [477.0], allergic rhinitis due to food [477.1], allergic rhinitis due to animal hair and dander [477.2], allergic rhinitis due to other allergen [477.8], and allergic rhinitis with cause unspecified [477.9]), breast cancer (ICD-9-CM code 174), cervical cancer (ICD-9-CM code 180), and ovarian cancer (ICD-9-CM code 183.0).

Statistical analysis

The differences between uterine leiomyoma and control groups were examined by Chi-square testing for categorical variables and the Student’s t-test for continuous variables. The Cox’s proportional hazards model was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for assessing the risk of endometriosis-associated uterine leiomyoma. Multivariable models were adjusted for age and other comorbidities as mentioned above. The Kaplan-Meier method assessed the cumulative incidence of endometriosis in women with uterine leiomyoma and controls; the log-rank test determined the significance of difference between the two groups. A two-tailed p-value of <0.05 was considered statistically significant. We used SAS software (version 9.4 for Windows; SAS Institute Inc., Cary, NC, USA) for all data analyses.

Results

We identified 31,239 women with uterine leiomyoma (cases) and 124,956 without leiomyoma (controls). Baseline variables for the study participants are shown in Table 1. Mean follow-up was 6.78±4.15 years for patients with uterine leiomyoma and 7.67±3.83 years for controls. Compared with controls, patients with uterine leiomyoma had significantly higher rates of endometritis, infertility, allergic diseases and breast cancer (p<0.001 for all comparisons). The incidence of cervical cancer was significantly lower in patients with leiomyoma than in controls (p<0.001).

Table 1

Baseline variables for patients with uterine leiomyoma and controls.

Variable	Uterine leiomyoma				p-value
	No (n = 124,956)		Yes (n = 31,239)
	N	%	n	%
Mean age (years, ±SD) a	41.9±9.10		42.5±8.23		0.77
Age (years)
20–39	46,052	36.9	11,119	35.6
40–49	60,692	48.6	15,567	49.8
≥50	18,212	14.6	4,553	14.6
Comorbidities
Tube-ovarian infection	38	0.03	7	0.02	0.46
Endometritis	6,008	4.81	2,354	7.54	<0.001
Infertility	4,803	3.84	1,729	5.53	<0.001
Autoimmune diseases	312	0.25	80	0.26	0.84
Allergic diseases	22,258	17.8	6,735	21.6	<0.001
Cancer	966	0.77	283	0.91	0.02
Breast cancer	670	0.54	266	0.85	<0.001
Cervical cancer	271	0.22	13	0.04	<0.001
Ovarian cancer	25	0.02	4	0.01	0.40
Follow-up (years) mean±SD	7.67±3.83		6.78±4.15		<0.001

SD = standard deviation. Chi-square test

a Student’s t-test.

In adjusted analyses, the risk of developing endometriosis was significantly higher among patients with uterine leiomyoma than controls (adjusted HR [aHR] 6.44; 95% CI, 6.18, 6.72). Comorbidities that were significantly associated with endometriosis included tube-ovarian infection (aHR 2.86; 95% CI, 1.28, 6.36), endometritis (1.14; 1.06, 1.24), infertility (1.26; 1.16, 1.37), and allergic diseases (1.11; 1.05, 1.17) (Table 2).

Table 2

Crude and adjusted risks of developing endometriosis associated with uterine leiomyoma.

Variable	Endometriosis (n = 9,021)	Crude HR†			Adjusted HR††
			(95% CI)	p-value		(95% CI)	p-value
Uterine leiomyoma
No	3,705	1.00	Reference		1.00	Reference
Yes	5,316	6.31	(6.05, 6.58)	<0.001	6.44	(6.18, 6.72)	<0.001
Age (years)
20–39	4,268	1.00	Reference		1.00	Reference
40–49	4,409	4.99	(4.47, 5.57)	<0.001	5.00	(6.04, 6.57)	<0.001
≥50	344	3.75	(3.36, 4.18)	<0.001	3.75	(3.36, 4.18)	<0.001
Comorbidity
Tube-ovarian infection
No	9,015	1.00	Reference	0.02	1.00	Reference	0.01
Yes	6	2.60	(1.17, 5.79)		2.86	(1.28, 6.36)
Endometritis
No	8,361	1.00	Reference	<0.001	1.00	Reference	<0.001
Yes	660	1.56	(1.44, 1.69)		1.14	(1.06, 1.24)
Infertility
No	8,432	1.00	Reference	<0.001	1.00	Reference	<0.001
Yes	589	1.81	(1.67, 1.97)		1.26	(1.16, 1.37)
Autoimmune diseases
No	9,001	1.00	Reference	0.80	1.00	Reference
Yes	20	0.95	(0.61, 1.47)
Allergic diseases
No	7,220	1.00	Reference	<0.001	1.00	Reference	<0.001
Yes	1801	1.27	(1.20, 1.34)		1.11	(1.05, 1.17)
Breast cancer
No	8,993	1.00	Reference	0.003	1.00	Reference	0.02
Yes	28	0.58	(0.40, 0.84)		0.64	(0.44, 0.93)
Cervical cancer
No	9,021	1.00	Reference		1.00	Reference	1.00
Yes	0	-	-		-	-	-
Ovarian cancer
No	9,021	1.00	Reference		1.00	Reference	1.00
Yes	0

HR = hazard ratio; CI = confidence interval.

The crude HR represents the relative hazard ratio without adjustment for age and comorbidities.

Variables found to be statistically significant in the univariable model were further examined in the multivariable model adjusted for age and comorbidities of tube-ovarian infection, endometritis, infertility, autoimmune diseases, allergic diseases, and breast cancer.

As shown in Table 3, the incidence rate of endometriosis in patients with uterine leiomyoma was 25.1 per 1,000 person-years, compared with 3.87 per 1,000 person-years in the control group. In fully adjusted analyses stratified by age and comorbidities, the risk of endometriosis was consistently significantly higher for those with uterine leiomyoma than for controls.

Table 3

Incidence rates and risk of endometriosis for patients with and without uterine leiomyoma, stratified by demographic variables and comorbidities.

Variables	Uterine leiomyoma						Compared to patients without uterine leiomyoma
	No			Yes			Crude HR†	Adjusted HR††
	(n = 124,956)			(n = 31,239)
	Event	Person- years	IR†	Event	Person- years	IR†	(95% CI)	(95% CI)
Total	3,705	957,831	3.87	5,316	211,858	25.1	6.31 (6.05, 6.58)***	6.44 (6.18, 6.72)***
Age group
20–39	1,905	343,497	5.55	2,363	72,458	32.6	5.76 (5.42, 6.12)***	5.65 (5.32, 6.01)***
40–49	1,753	478,685	3.66	2,656	107,239	24.8	6.51 (6.13, 6.92)***	6.46 (6.08, 6.86)***
≥50	47	135,650	0.35	297	32,161	9.23	26.2 (19.3, 35.6)***	26.2 (19.2, 35.6)***
Comorbidities
No	2,600	764,399	3.40	3,697	154,990	23.9	6.85 (6.51, 7.20)***	7.13 (6.78, 7.50)***
Yes	1,105	193,433	5.71	1,619	56,867	28.5	4.94 (4.58, 5.33)***	5.09 (4.72, 5.50)***

IR = incidence rates per 1,000 person-years; HR = hazard ratio; CI = confidence interval.

†The crude HR represents the relative hazard ratio without adjustment for age and comorbidities.

††Variables found to be statistically significant in the univariable model were further examined in the multivariable model adjusted for age and comorbidities of tube-ovarian infection, endometritis, infertility, autoimmune diseases, allergic diseases, and breast cancer.

*p<0.05; **p<0.01

***p<0.001.

The data in Table 4 reveal a synergistic effect between uterine leiomyoma and comorbidities for the risk of endometriosis. Patients with both uterine leiomyoma and endometritis had a higher risk of developing endometriosis (aHR 6.73; 95% CI, 6.07, 7.45) than those with uterine leiomyoma alone (6.61; 6.33, 6.91) or endometritis alone (1.49; 1.31, 1.69). Similarly, patients with both uterine leiomyoma and infertility had a higher risk of endometriosis (aHR 6.95; 95% CI, 6.21, 7.78) than those with uterine leiomyoma only (6.66; 6.38, 6.96) or infertility only (1.78; 1.57, 2.02). No such synergistic effects were observed for allergic diseases and breast cancer; patients with uterine leiomyoma were apparently at significantly higher risk of developing endometriosis, whether or not they had either of those comorbidities.

Table 4

Cox’s proportional hazard regression analysis identified a synergistic effect between uterine leiomyoma and comorbidities for the risk of endometriosis.

Variables		No.	Endometriosis	Adjusted HR†	p-value#
			No.	(95% CI)
Uterine leiomyoma	Endometritis				<0.001
No	No	118,948	3,454	1 (Reference)
No	Yes	6,008	251	1.49 (1.31, 1.69)***
Yes	No	28,885	497	6.61 (6.33, 6.91)***
Yes	Yes	2,354	409	6.73 (6.07, 7.45)***
Uterine leiomyoma	Infertility				<0.001
No	No	120,153	3,451	1 (Reference)
No	Yes	4,803	254	1.78 (1.57, 2.02)***
Yes	No	29,510	4,981	6.66 (6.38, 6.96)***
Yes	Yes	1,729	335	6.95 (6.21, 7.78)***
Uterine leiomyoma	Allergic diseases				<0.001
No	No	102,698	2,959	1 (Reference)
No	Yes	22,258	746	1.29 (1.19, 1.40)***
Yes	No	24,504	4,261	6.79 (6.48, 7.12)***
Yes	Yes	6,735	1,055	6.70 (6.24, 7.19)***
Uterine leiomyoma	Breast cancer				0.63
No	No	124,286	3,698	1 (Reference)
No	Yes	670	7	0.54 (0.26, 1.12)
Yes	No	30,973	5,295	6.44 (6.17, 6.72)***
Yes	Yes	266	21	4.27 (2.78, 6.56)***

HR = hazard ratio; CI = confidence interval.

†The Cox’s model was adjusted for age and comorbidities of tube-ovarian infection, endometritis, infertility, autoimmune diseases, allergic diseases, and breast cancer.

*p<0.05; **p<0.01

***p<0.001.

As illustrated in Fig 2, Kaplan-Meier analysis revealed that the cumulative incidence of endometriosis was significantly higher in patients with uterine leiomyoma than in those without (log-rank test, p<0.001).

Fig 2

Kaplan-Meier analysis of endometriosis risk in patients with and without uterine leiomyoma.

HR = hazard ratio; CI = confidence interval.

Discussion

This large-scale nationwide study from Taiwan with 14 years of follow-up reveals that women at any age with uterine leiomyoma appear to be at significantly increased risk of developing endometriosis. Endometriosis and uterine fibroids are common disorders that affect significant numbers of women. Previous studies have identified incidence rates of between 12% and 20% for concomitant fibroids and endometriosis [25, 30]. In a US study, 87% of 208 patients who underwent surgical treatment for symptomatic leiomyoma were found to have endometriosis [31]. Endometriosis poses a significantly high economic burden, both before and after diagnosis. A large longitudinal analysis of US healthcare claims databases observed that women with endometriosis experienced significantly higher annual healthcare costs compared with women without endometriosis, with an overall cost difference of $26,305 (in 2010 US dollars) over 10 years; $7,028 in the 5 years before diagnosis and $19,277 in the 5 years after diagnosis [30]. It is important to evaluate the risk factors for endometriosis, to slow the inflammatory process and prevent the development of endometriosis. Early diagnosis and treatment of endometriosis might lessen the healthcare burden of this chronic disease.

To our knowledge, our research is the largest population-based longitudinal study with long-term follow-up to have examined the potential association between uterine leiomyoma and endometriosis. Our findings reveal that a strong association appears to exist between uterine leiomyoma and endometriosis. Our recent confirmation of an increased risk of endometriosis in patients with endometritis [32] led us to include endometritis as a potential confounder in this study. When we compared baseline disease variables between women with uterine leiomyoma and those without, we found significantly higher rates of endometritis, infertility and allergic diseases in the uterine leiomyoma cohort; in analyses that adjusted for all potential confounders, the risk of developing endometriosis was significantly higher in patients with uterine leiomyoma. Uterine leiomyoma was associated with a significantly increased risk of developing endometriosis in all age groups (20–39 years, 40–49 years, ≥50 years).

The reasons for the apparently strong association between leiomyoma and endometriosis are unclear. Researcher groups have identified risk factors for the coexistence of myomas and endometriosis, including younger age, nulliparity, moderate-to-severe pain, short menstrual intervals, smaller myomas, and locations of myomas [26, 33]. Our hypothesis is that uterine leiomyoma could predispose to retroverted uterus or distort the uterine cavity, increasing the risk of retrograde menstruation and thus increasing the risk of developing endometriosis. To support our theory, further studies are needed to investigate whether the numbers, sizes or locations of uterine leiomyoma impact differently on the risk of developing endometriosis.

It is well known that infertile women have a higher prevalence of endometriosis and are significantly more likely than fertile women to have moderate-to-severe endometriosis [34]. Similarly, our findings showed that women with infertility problems have an almost 2-fold greater risk of developing endometriosis, which increased to almost 7-fold in women with infertility and uterine leiomyoma. Having both comorbidities synergistically increased the risk of developing endometriosis compared with women with infertility or uterine leiomyoma alone. Similarly, the risk for developing endometriosis was synergistically increased in women with uterine leiomyoma and endometritis. However, no such synergistic effect was observed among women with the comorbidities of breast cancer and allergic diseases.

This study has a number of strengths. It obtained data from a large number of participants from throughout Taiwan and provided long-term follow-up, allowing a high statistical power calculation (>0.9) for ascertaining an association between uterine leiomyoma and endometriosis. Stratified sensitivity analyses performed to clarify misclassifications and potential confounders did not reveal any significant changes in HRs between the different models. The potential association among uterine leiomyoma, endometriosis and other comorbidities has never previously been examined. Interestingly, our results demonstrated that a synergistic effect exists amongst these disorders.

There are some limitations with this study. The NHIRD dataset is not able to provide detailed demographic information in regard to laboratory results, levels of physical activity, or any family medical history, any of which may affect the apparent association observed between uterine leiomyoma and endometriosis. Moreover, the level of severity of endometriosis or uterine leiomyoma could not be analyzed from the NHIRD data. Another limitation is that in Taiwan, the oral contraceptive pill may be obtained over the counter, and it is not uncommon for women to purchase Chinese medicines, some of which may contain phytoestrogens with unknown clinical therapeutic effects. This sort of information is not provided by the NHIRD database. However, our large sample size in this study may offset any population variation. The apparent relationship between leiomyoma, endometriosis and hormonal therapy can be further explored in future studies.

As for the practical implications in regard to the apparent association between uterine leiomyoma and endometriosis, clinicians need to be aware of the symptoms that patients may experience. Endometriosis should be suspected in women who have uterine leiomyoma with a history of endometriosis or infertility. It is important for clinicians to have preoperative discussions with a patient undergoing elective surgery for uterine leiomyoma, in order to gain prior informed consent for removal of endometrial tissue discovered during surgery. Lastly, for an infertile couple who is considering in vitro fertilization (IVF) or who has experienced unsuccessful IVF attempts, ultrasound examinations should look for evidence of leiomyoma and endometriosis.

Conclusion

In conclusion, women at any age with uterine leiomyoma appear to be at significantly increased risk of developing endometriosis. The presence of uterine leiomyoma with other comorbidities, such as infertility or endometritis, synergistically increases the risk for endometriosis. Failure to diagnose and treat all etiologies of a patient’s symptoms may lead to higher treatment failure rates as well as an increased recurrence rate. Early recognition and treatment of endometriosis among women with uterine leiomyoma may improve the clinical outcome, slow the progression of endometriosis and alleviate the healthcare burden of this chronic disease.

4 May 2021

PONE-D-21-09322

Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women

PLOS ONE

Dear Dr. Yang,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Jun 18 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Antonio Simone Laganà, M.D., Ph.D.

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Thank you for stating the following in the Funding Section of your manuscript:

This study was supported in part by Taiwan’s Ministry of Health and Welfare Clinical Trial Center (MOHW109-TDU-B-212-114004), the MOST Clinical Trial Consortium for Stroke (MOST 108-2321-B-039-003-) and the Tseng-Lien Lin Foundation, Taichung, Taiwan.

We note that you have provided funding information that is not currently declared in your Funding Statement. However, funding information should not appear in the Acknowledgments section or other areas of your manuscript. We will only publish funding information present in the Funding Statement section of the online submission form.

Please remove any funding-related text from the manuscript and let us know how you would like to update your Funding Statement. Currently, your Funding Statement reads as follows:

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Please include your amended statements within your cover letter; we will change the online submission form on your behalf.

Please include captions for your Supporting Information files at the end of your manuscript, and update any in-text citations to match accordingly. Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information.

Additional Editor Comments:

The topic of the manuscript is interesting. Nevertheless, the reviewers raised several concerns: considering this point, I invite authors to perform the required major revisions.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: PONE-D-21-09322

The manuscript entitled “Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women” analyzed the association between uterine leiomyoma and the increased risk for endometriosis.

The study is well written and the material and methods are correctly used. I suggest few corrections as detailed below:

In the Introduction, Authors should underline the role of quality of life in endometriosis, briefly referring to PMID: 31755667, PMID: 30269659, and PMID: 31726815

The first sentence of the Discussion should explain the main findings of the study.

Reviewer #2: I was pleased to review the Research Article “Uterine leiomyoma in associated with the risk of developing endometriosis: a nationwide cohort study involving 156, 195 women.” from PLOS ONE.

The methodology used by the Authors is appropriate for the purpose of the study and conclusions are narrow linked to data discussion and available evidence. The English language is fluid and well understood. Nevertheless, major revision is needed, but the paper is of good quality.

I suggest this:

1. Abstract: is complete and well written.

2. Introduction: I really appreciated the quote over the theory about retrograde menstruation, and it is important to emphasize the association, as you have done, concerning estrogenic dysregulation: uterine leiomyoma and endometriosis are hormone-dependent. I suggest taking into account these papers to improve the quality of this section: doi: 10.3390/ijerph17134683; doi: 10.1093/biolre/ioab054.

3. Material and Methods. the strong point of the work structure is the big data source comprised the Longitudinal Health Insurance Database 2000 and the study participants with women aged > 20 years between 2000 and 2012.

4. Results. I have some questions.

• Were patients with endometritis treated? if yes, how?

• When you talk about the association between leiomyoma and infertility which increases the risk of endometriosis, what about the patients who had infertility problems in detail?

• When you define the non-synergy on the risks associated with allergies, what kind of allergies are we talking about?

• When you talk about non-synergy with breast cancer, did the patients have BRCA mutations?

5. Discussion. Good ideas for future work, as this leiomyoma-endometriosis association is clear…but why…this exists, not yet.

Also as you wrote, the database does not contain: demographic details, levels of physical activity, or any family medical history, another weak point as you said, is the level of severity of endometriosis or uterine leiomyoma could not be analyzed, another point is the not uncommon use for these women of the oral contraceptive pill.

6. Conclusion. I found the conclusions coherent with the work done. Excellent reflection for an infertile couple who is considering IVF to investigate the presence of leiomyoma/endometriosis.

Reviewer #3: I was pleased to revise the manuscript entitled “Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women” (Manuscript Number: PONE-D-21-09322).

Taiwan’s Ministry of Health and Welfare Clinical Trial Center (MOHW109-TDU-B-212-114004), the MOST Clinical Trial Consortium for Stroke (MOST 108-2321-B-039-003-) and the Tseng-Lien Lin Foundation, Taichung, Taiwan approved the study.

In my honest opinion, the topic is interesting enough to attract the readers’ attention. Nevertheless, the manuscript may benefit from major revisions:

- The text needs a language revision to improve the readability, some typos, and some grammatical errors.

- Abstract. The retrospective study design cannot support the conclusion that the risk of endometriosis is increased by uterine leiomyoma. Based on the study methods, it is correct to refer only to the “association” between a diagnosis of leiomyoma and endometriosis.

- I would suggest checking the use of abbreviation that should be reported in the extended form at the first use in the abstract, text, and tables.

- Please, clarify which type of diagnosis of myoma were included. Any modality?

- The used study methods cannot provide an answer to the question of whether having uterine leiomyoma increases the risk of developing endometriosis. Only an association is observable. A cause-effect relationship is not possible. Please, revise the used terms.

- Lines 131-134. Please, clarify what you mean by “who did not have a recorded diagnosis of uterine leiomyoma”. If you refer that matched cohort did not diagnose uterine myomas for the entire study period, this is wrong. Matched cohort should include women without a diagnosis of myoma up to the index date; otherwise, you introduce a bias in the study design if myomas cannot be diagnosed later. Indeed, an appropriate study design can include patients both as exposed and unexposed. One patient should be matched with women that the index year who had the same age and not a diagnosis of myoma. These women can become exposed cohort when 5 years later have a diagnosis of myoma and will be matched with women that the index date (year of myoma diagnosis) have the same age and never had a diagnosis of myoma. Differently, in the matched cohort, you are artificially selecting women who will never develop myoma, which is not natural considering the high proportion of women who in life develop uterine fibroids.

- Lines 180-188. I would suggest better clarifying these study results. The association regarding time relationship.

- Please, report HR and 95%CI in all cases.

- Abstract and lines 263-267. This statement is unclear because in the present study, cases with a diagnosis of endometriosis concomitant to the diagnosis of myoma were excluded (figure 1).

- I would suggest discussing better, at least briefly, the therapeutic options for endometriosis and its pathogenesis. Refer to PMID: 32046116; PMID: 31532753; PMID: 33096011; PMID: 32981374

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

9 Jul 2021

Reference: PONE-D-21-09322

Academic Editor, PLOS One

Dear Dr. Laganà

We greatly appreciate the comments from your Reviewers on our manuscript Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women (Ref.: PONE-D-21-09322).

We have carefully revised the manuscript according to the suggestions raised by the Reviewers; specific points are addressed below. We have marked up our changes using red font in the revised manuscript.

We sincerely hope that our revised manuscript is now suitable for publication in PLOS One.

Yours sincerely,

Kent Yu-Hsien Lin (M.B.B.S., M.Med) and Chih-Yi Yang (M.D.)

Reviewer #1: PONE-D-21-09322

The manuscript entitled Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women analyzed the association between uterine leiomyoma and the increased risk for endometriosis.

The study is well written and the material and methods are correctly used. I suggest few corrections as detailed below:

In the Introduction, Authors should underline the role of quality of life in endometriosis, briefly referring to PMID: 31755667, PMID: 30269659, and PMID: 31726815

The first sentence of the Discussion should explain the main findings of the study.

Response: We thank the Reviewer for this constructive feedback, which has enabled us to improve our manuscript. We have accordingly amended the Introduction and Discussion, as follows:

These symptoms can have enormous impact on a sufferer’s quality of life, with well-documented evidence describing how these symptoms interfere with daily life and activities, adversely affecting general health and psychological well-being, and impacting on overall sexual functioning (13-15). (Lines 77-80)

This large-scale nationwide study from Taiwan with 14 years of follow-up reveals that women at any age with uterine leiomyoma appear to be at significantly increased risk of developing endometriosis. (Lines 228-230)

Reviewer #2: I was pleased to review the Research Article Uterine leiomyoma in associated with the risk of developing endometriosis: a nationwide cohort study involving 156, 195 women. from PLOS ONE.

The methodology used by the Authors is appropriate for the purpose of the study and conclusions are narrow linked to data discussion and available evidence. The English language is fluid and well understood. Nevertheless, major revision is needed, but the paper is of good quality.

Response: We thank the Reviewer for this thoughtful, appreciative feedback on our manuscript.

Reviewer #2: I suggest this:

1. Abstract: is complete and well written.

Response: We thank the Reviewer for this approval of the Abstract.

2. Introduction: I really appreciated the quote over the theory about retrograde menstruation, and it is important to emphasize the association, as you have done, concerning estrogenic dysregulation: uterine leiomyoma and endometriosis are hormone-dependent. I suggest taking into account these papers to improve the quality of this section: doi: 10.3390/ijerph17134683; doi: 10.1093/biolre/ioab054.

Response: We thank the Reviewer for these insightful suggestions and we have accordingly amended our text, adding more references in regard to the adverse impact of endometriosis-related symptoms on quality of life, as this was called for by another Reviewer as well. Our amended section in the Introductory text is as follows:

Endometriosis is another common gynecological condition, affecting 10–50% of reproductive-aged women (7-9). The most common symptoms are dysmenorrhea, chronic pelvic pain, dyspareunia and subfertility (10-12). These symptoms can have enormous impact on a sufferer’s quality of life, with well-documented evidence describing how these symptoms interfere with daily life and activities, adversely affecting general health and psychological well-being, and impacting on overall sexual functioning (13-15). Moreover, endometriosis-related symptoms impose a substantial economic burden on those afflicted in terms of direct costs of medical care and indirect costs, such as costs for sick leave and work absenteeism (14, 16). It is well known that the risk of endometriosis is higher in young women with menstrual dysfunction and any obstruction to the outflow of menstrual products (17, 18). This is thought to be because of the higher volume of refluxed menstrual blood and endometrial tissue fragments, lending support to the theory that endometriosis results from retrograde menstruation (17). Genetic insights, the possible roles of the environment and the immune system, as well as intrinsic abnormalities in the endometrium of affected women have helped to elucidate the pathogenesis of endometriosis (19). Endometriosis is an estrogen-dependent disorder. Recent speculations suggest that the estrogen-dependent activity of different ion channels may contribute to the etiology of endometriosis (20). The levels of estrogen expression and functionality of these ion channels fluctuate between menstrual phases, with increased estrogen enhancing pathogenic aspects of endometriosis, such as the proliferation and in vivo implantation of ectopic endometrium (20). More evidence is needed to determine the strength of this association. Available conventional therapeutic strategies for managing endometriosis (surgery, hormonal treatment, nonsteroidal anti-inflammatories) have limited or intermittent efficacy, as well as unwanted hormonal side effects such as the loss of bone density (21). Aromatase inhibitors (AIs) have been proposed for endometriosis treatment, with limited clinical data indicating associated reductions in volume and symptoms of endometrioma, but AIs have also been linked to the development of functional cysts and menopausal symptoms, as well as reductions in bone mineral density (22). Alternative progestins and estroprogestins drug delivery methods (e.g., vaginal rings, patches, subcutaneous implants, intrauterine drug delivery systems, nanotechnologies) offer potential advantages of fewer adverse events, greater therapeutic efficacy, improved patient compliance and satisfaction (23). At this point, more clinical experience is needed before any conclusions can be made about the clinical efficacies of these alternative drug delivery methods (23). Thus, the disadvantages of current pharmacotherapeutic options have induced many women with endometriosis to seek alternative treatment options, such as phytotherapy (21, 24). Promisingly, in vitro and preclinical investigations have indicated that some phytochemicals demonstrate strong phytoestrogenic effects capable of modulating estrogen and inflammatory activity, which could help to reduce endometriosis symptoms, although randomized controlled trial data are lacking (21, 24). Interestingly, increasing clinical and pathophysiological evidence supports the notion that chronic inflammation is associated with benign gynecological disorders such as uterine leiomyoma and endometriosis (25). These associations have been comprehensively reviewed (25), although basic and clinical investigations have yet to clearly define the mechanism responsible for the development of endometriosis. Up until now, research has focused on altered immune responses and other regulatory factors that may mediate the histogenesis of endometriosis. (Lines 77-118)

3. Material and Methods. the strong point of the work structure is the big data source comprised the Longitudinal Health Insurance Database 2000 and the study participants with women aged > 20 years between 2000 and 2012.

Response: We thank the Reviewer for highlighting the fact that the body of evidence from the LHID2000 lends weight to our study.

4. Results. I have some questions.

(i) Were patients with endometritis treated? if yes, how?

(ii) When you talk about the association between leiomyoma and infertility which increases the risk of endometriosis, what about the patients who had infertility problems in detail?

(iii) When you define the non-synergy on the risks associated with allergies, what kind of allergies are we talking about?

(iv) When you talk about non-synergy with breast cancer, did the patients have BRCA mutations?

Responses:

(i) Our endometritis data were collected according to coding by the International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM code 615), classifying the disease by the patient’s signs and symptoms. Indeed, all patients were treated with antibiotics.

(ii) Our infertility data were collected according to coding by the International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM code 628), classifying the disease by the patient’s history and symptoms. Unfortunately, we are unable to collect the different causes of infertility in our database. Our Discussion section mentions that in patients with infertility problems, ultrasound examinations should look for evidence of leiomyoma and endometriosis. (Lines 302-305)

(iii) For allergic diseases, we used ICD-9-CM code 477, allergic rhinitis, which includes allergic rhinitis due to pollen (477.0), allergic rhinitis due to food (477.1), allergic rhinitis due to animal hair and dander (477.2), allergic rhinitis due to other allergen (477.8), and allergic rhinitis with cause unspecified (477.9). We have now added this information to the manuscript, to clarify for the readers what we mean by “allergic diseases”. (Lines 177-179)

(iv) According to ICD-9-CM coding, we included all types of breast cancers in our study, which include but are not limited to estrogen receptor-positive, progesterone receptor-positive, hormone receptor-negative, HER2-positive, BRCA mutations, and so on.

5. Discussion. Good ideas for future work, as this leiomyoma-endometriosis association is clear &but why &this exists, not yet.

Also as you wrote, the database does not contain: demographic details, levels of physical activity, or any family medical history, another weak point as you said, is the level of severity of endometriosis or uterine leiomyoma could not be analyzed, another point is the not uncommon use for these women of the oral contraceptive pill.

Response: We greatly appreciate the Reviewer’s close attention to our work.

6. Conclusion. I found the conclusions coherent with the work done. Excellent reflection for an infertile couple who is considering IVF to investigate the presence of leiomyoma/endometriosis.

Response: We sincerely thank the Reviewer for this endorsement of our concluding recommendations.

Reviewer #3: I was pleased to revise the manuscript entitled Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women (Manuscript Number: PONE-D-21-09322).

Taiwan’s Ministry of Health and Welfare Clinical Trial Center (MOHW109-TDU-B-212-114004), the MOST Clinical Trial Consortium for Stroke (MOST 108-2321-B-039-003-) and the Tseng-Lien Lin Foundation, Taichung, Taiwan approved the study.

In my honest opinion, the topic is interesting enough to attract the readers attention.

Response: We thank the Reviewer for this endorsement of our work.

Reviewer #3: Nevertheless, the manuscript may benefit from major revisions:

- The text needs a language revision to improve the readability, some typos, and some grammatical errors.

Response: The manuscript has been edited by a native English speaker who also has several years of medical editing and writing experience.

- Abstract. The retrospective study design cannot support the conclusion that the risk of endometriosis is increased by uterine leiomyoma. Based on the study methods, it is correct to refer only to the association between a diagnosis of leiomyoma and endometriosis.

Response: We thank the Reviewer for making this point and we have accordingly amended our Abstract conclusion text as follows:

A diagnosis of uterine leiomyoma appears to increase the risk of endometriosis. (Lines 64-65)

- I would suggest checking the use of abbreviation that should be reported in the extended form at the first use in the abstract, text, and tables.

Response: Thank you for paying such close attention to our text. We have accordingly checked all of the text and amended it wherever necessary where an abbreviation needed to be defined at first mention.

- Please, clarify which type of diagnosis of myoma were included. Any modality?

Response: Four types of myoma were included: submucosal; intramural; subserosal; and pedunculated. Any type of myoma was included in our study and all were diagnosed by ultrasound or surgical methods.

- The used study methods cannot provide an answer to the question of whether having uterine leiomyoma increases the risk of developing endometriosis. Only an association is observable. A cause-effect relationship is not possible. Please, revise the used terms.

Response: We thank the Reviewer for pointing this out and we have accordingly revised the conclusions text in the Abstract, text in the Results section, and text in the Discussion. (Lines 64-65, 221, 229, 245-246, 257, 281, 294, 297, 308 and 313)

- Lines 131-134. Please, clarify what you mean by who did not have a recorded diagnosis of uterine leiomyoma. If you refer that matched cohort did not diagnose uterine myomas for the entire study period, this is wrong. Matched cohort should include women without a diagnosis of myoma up to the index date; otherwise, you introduce a bias in the study design if myomas cannot be diagnosed later. Indeed, an appropriate study design can include patients both as exposed and unexposed. One patient should be matched with women that the index year who had the same age and not a diagnosis of myoma. These women can become exposed cohort when 5 years later have a diagnosis of myoma and will be matched with women that the index date (year of myoma diagnosis) have the same age and never had a diagnosis of myoma. Differently, in the matched cohort, you are artificially selecting women who will never develop myoma, which is not natural considering the high proportion of women who in life develop uterine fibroids.

Response: Our matched cohort (control group) only included women without a diagnosis of myoma up to the index date, which means that for every individual woman with no history of myoma up to the index date, we commenced her follow-up and continued until the end of 2012, to determine whether she developed endometriosis during the follow-up period. We followed-up 124,956 women in our control group.

- Lines 180-188. I would suggest better clarifying these study results. The association regarding time relationship.

Response: To explain clearly how we calculated mean follow-up years, we can use the study group (leiomyoma group) as an example:

If a woman who had no pre-existing endometriosis disease was diagnosed with uterine leiomyoma in 2001, we followed-up this particular woman for years and realized that she developed endometriosis in 2011. Her follow-up time would thus be 11 years. On the other hand, if a woman without pre-existing endometriosis was diagnosed with leiomyoma in 2009 and we were only able to follow her until the end of 2012, her follow-up time would be 4 years. The average of the follow-up times in these two women is 7.5 years (11 years + 4 years = 15 years, divided by 2 = 7.5 years). The mean follow-up in these two women as our study group would thus be 7.5 years. Instead of using just two women, our study used follow-up times from 31,239 women to calculate the mean, arriving at 6.78 +/- 4.15 years in our study group (leiomyoma group). For the control group, as per the above, by matching the age and the year of diagnosis, we used 124,956 women to calculate the mean follow-up time, arriving at 7.67 +/- 3.83 years.

- Please, report HR and 95%CI in all cases.

Response: We have accordingly enriched the Abstract text with adjusted HR and 95% CI values, which was the only place in the manuscript that had not reported all such values. Table 1 cannot provide HR/95% CI values, but does report p-values, which are essentially the same as 95% CIs.

- Abstract and lines 263-267. This statement is unclear because in the present study, cases with a diagnosis of endometriosis concomitant to the diagnosis of myoma were excluded (figure 1).

Response: The aim of this research was to determine whether the presence of leiomyoma would increase the risk of developing endometriosis. Figure 1 includes 1 million patients randomly selected from our database. Among those 1 million patients, 44,924 patients had ‘newly’ diagnosed uterine leiomyoma. A total of 5,883 patients with a pre-existing diagnosis of endometriosis were excluded. Along with our exclusion criteria (7,713 + 4 + 85 = 7,802 patients), this yielded only 31,239 patients with uterine leiomyoma to conduct the follow-up study (44,924 – 7,802 – 5,883 = 31,239 patients). The follow-up study revealed for us the information that leiomyoma increases the risk of developing endometriosis. Hence, we suggested that women with infertility should look for underlying risk factors such as endometriosis and leiomyoma (as women with leiomyoma were likely to have endometriosis, according to our study evidence).

- I would suggest discussing better, at least briefly, the therapeutic options for endometriosis and its pathogenesis. Refer to PMID: 32046116; PMID: 31532753; PMID: 33096011; PMID: 32981374

Response: We thank the Reviewer for this suggestion, which enables us to improve our text. We have accordingly amended the Introduction to read as follows:

Genetic insights, the possible roles of the environment and the immune system, as well as intrinsic abnormalities in the endometrium of affected women have helped to elucidate the pathogenesis of endometriosis (19). Endometriosis is an estrogen-dependent disorder. Recent speculations suggest that the estrogen-dependent activity of different ion channels may contribute to the etiology of endometriosis (20). The levels of estrogen expression and functionality of these ion channels fluctuate between menstrual phases, with increased estrogen enhancing pathogenic aspects of endometriosis, such as the proliferation and in vivo implantation of ectopic endometrium (20). More evidence is needed to determine the strength of this association. Available conventional therapeutic strategies for managing endometriosis (surgery, hormonal treatment, nonsteroidal anti-inflammatories) have limited or intermittent efficacy, as well as unwanted hormonal side effects such as the loss of bone density (21). Aromatase inhibitors (AIs) have been proposed for endometriosis treatment, with limited clinical data indicating associated reductions in volume and symptoms of endometrioma, but AIs have also been linked to the development of functional cysts and menopausal symptoms, as well as reductions in bone mineral density (22). Alternative progestins and estroprogestins drug delivery methods (e.g., vaginal rings, patches, subcutaneous implants, intrauterine drug delivery systems, nanotechnologies) offer potential advantages of fewer adverse events, greater therapeutic efficacy, improved patient compliance and satisfaction (23). At this point, more clinical experience is needed before any conclusions can be made about the clinical efficacies of these alternative drug delivery methods (23). Thus, the disadvantages of current pharmacotherapeutic options have induced many women with endometriosis to seek alternative treatment options, such as phytotherapy (21, 24). Promisingly, in vitro and preclinical investigations have indicated that some phytochemicals demonstrate strong phytoestrogenic effects capable of modulating estrogen and inflammatory activity, which could help to reduce endometriosis symptoms, although randomized controlled trial data are lacking (21, 24). Interestingly, increasing clinical and pathophysiological evidence supports the notion that chronic inflammation is associated with benign gynecological disorders such as uterine leiomyoma and endometriosis (25). These associations have been comprehensively reviewed (25), although basic and clinical investigations have yet to clearly define the mechanism responsible for the development of endometriosis. (Lines 86-116)

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

16 Aug 2021

Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women

PONE-D-21-09322R1

Dear Dr. Yang,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Antonio Simone Laganà, M.D., Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Authors performed the required corrections, which were positively evaluated by the reviewers. I am pleased to accept this paper for publication.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The Authors improved the manuscript as requested. I suggest the acceptance of the manuscript in the present form.

Kind regards

Reviewer #2: Good job, all changes have been performed as requested. I only ask you to check the reference list in order to avoid duplicate

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

18 Aug 2021

PONE-D-21-09322R1

Uterine leiomyoma is associated with the risk of developing endometriosis: a nationwide cohort study involving 156,195 women

Dear Dr. Yang:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Antonio Simone Laganà

Academic Editor

PLOS ONE