Efficacy of adjuvant chemotherapy with S-1 in stage II oral squamous cell carcinoma patients: A comparative study using the propensity score matching method.

It has been reported that 20% of early-stage oral squamous cell carcinoma (OSCC) patients treated with surgery alone (SA) may exhibit postoperative relapse within 2-3 years and have poor prognoses. We aimed to determine the safety of S-1 adjuvant chemotherapy and the potential differences in the disease-free survival (DFS) between patients with T2N0 (stage II) OSCC treated with S-1 adjuvant therapy (S-1) and those treated with SA. This single-center retrospective cohort study was conducted at Kumamoto University, between April 2004 and March 2012, and included 95 patients with stage II OSCC. The overall cohort (OC), and propensity score-matched cohort (PSMC) were analyzed. In the OC, 71 and 24 patients received SA and S-1, respectively. The time to relapse (TTR), DFS, and overall survival were better in the S-1 group, but the difference was not significant. In the PSMC, 20 patients each received SA and S-1. The TTR was significantly lower in the S-1 group than in the SA group, while the DFS was significantly improved in the former. S-1 adjuvant chemotherapy may be more effective than SA in early-stage OSCC.

Introduction

Oral cancer, and predominantly oral squamous cell carcinoma (OSCC), is a major cause of morbidity and mortality worldwide. The survival rate of these patients has not improved, despite advances and innovations in the diagnostic techniques and treatments used [1]. Locally advanced OSCC is generally associated with particularly poor prognoses owing to the difficulty in controlling it with surgery and adjuvant radiotherapy or concurrent chemoradiotherapy [2, 3]. However, even in case of early-stages disease (T1-2N0), which can be cured by therapy, more than 80% of the cases being subjected to curative surgery may exhibit postoperative relapse within the first 2 to 3 years [4, 5]. Therefore, it is essential to control local recurrence and/or regional lymph node metastasis to improve the patients’ prognoses.

S-1, a novel oral fluoropyrimidine preparation (Taiho Pharmaceutical, Tokyo, Japan), is designed to improve the antitumor activity of 5-FU, while also reducing gastrointestinal toxicity. S-1 contains tegafur (a prodrug of 5-FU), gimeracil (inhibits the 5-FU degeneration enzyme, dihydropyrimidine dehydrogenase), and oteracil (reduces the gastrointestinal toxicity of 5-FU) [6-8]. In patients with various cancers, including those of the head and neck, S-1 administered alone or in combination with other chemotherapeutic agents has been shown to improve the outcomes [9-12].

Recently, the Adjuvant Chemotherapy with S-1 after Curative Treatment in Patients with Head and Neck Cancer (ACTS-HNC) study, which enrolled patients with advanced head and neck squamous cell carcinoma (HNSCC), reported significantly better overall survival (OS) in the S-1 group than in the control group [13]. Furthermore, reports have confirmed the efficacy of S-1 after curative surgery in gastric and pancreatic cancer [10, 14, 15]. These results encouraged us to investigate whether S-1 could be considered as a treatment option after curative surgery in patients with OSCC, even in early-stage disease. The primary aim of this study was to evaluate the efficacy and safety of S-1 compared with surgery alone (SA) in patients with stage II OSCC.

Material and methods

Study population

The study population comprised patients with cT2N0 (stage II) OSCC. They were diagnosed based on the histological and radiological findings, including computed tomography (CT), magnetic resonance imaging, ultrasonography, and positron emission tomography-computed tomography (PET-CT) findings. All tumors were staged according to the TNM classification of the American Joint Committee on Cancer, 7th edition [16], and the degree of differentiation was determined according to the classification of the World Health Organization [17]. Histopathological tumor invasion phenotypes were categorized with respect to the mode of invasion [18]. In our department, elective neck dissection is only performed for cases of N0 oral cancer for the purpose of reconstruction, and a “wait-and-see policy” has been adopted. Therefore, all patients enrolled in the present study only underwent resection of the primary tumor. After completion of curative surgery, we confirmed whether the patients met the eligibility criteria. Those treated with SA and S-1 at the Department of Oral and Maxillofacial Surgery, Kumamoto University Hospital were enrolled from April 2004, with observation continuing until March 2012. This study was conducted with the approval of the Ethics Committee of Kumamoto University (approval number, 747), in accordance with the guidelines for Good Clinical Practice and the Declaration of Helsinki. All patients provided written informed consent before enrollment in the study.

Eligibility criteria

To further improve the outcomes in patients with early-stage OSCC, we began administering adjuvant chemotherapy with S-1 from 2004. The eligibility criteria for adjuvant chemotherapy with S-1 for patients with cT2N0 oral carcinoma were as follows: (1) curative surgery only for the primary tumor, (2) histologically verified SCC of the oral cavity, (3) no residual tumor (primary lesion) confirmed on diagnostic imaging or biopsy, (4) performance status of 0–1 and normal hematologic parameters (white blood cell count ≥ 3500/mm3, hemoglobin level ≥ 9.0 g/dL, and platelet count ≥ 100,000/mm3), liver function (total bilirubin level ≤ 1.5 mg/dL, and aspartate transaminase [AST] level and alanine transaminase [ALT] levels ≤ ULN×2.5), renal function (creatinine level ≤ 1.2 mg/dL and creatinine clearance ≥ 60 mL/min), and (5) absence of severe complications. In order to focus on evaluating the treatment efficacy of S-1, patients who underwent elective neck dissection and sentinel lymph node biopsies were excluded [19]. In addition, patients who previously received systemic therapy or radiotherapy and had distant metastasis, concomitant malignancies, active inflammatory disease, active gastric/duodenal ulcers, severe heart disease, or other severe concurrent disease were excluded. Pregnant or lactating women were also excluded.

Treatment

After the completion of curative surgery, patients who consented to undergo S-1 adjuvant chemotherapy were assigned to the S-1 group, and those who refused S-1 adjuvant chemotherapy were assigned to the SA group. In the S-1 group, patients received 80 mg/day (body surface area [BSA] < 1.25 m2), 100 mg/day (BSA ≥ 1.25 to < 1.5 m2), or 120 mg/day (BSA ≥1.5 m2) of S-1, in two divided doses, daily, for 2 weeks, followed by a 1-week period of rest [11]. Administration of S-1 was started within 8 weeks after surgery, and the duration of treatment was 1 year. If adverse events meeting the criteria for temporary treatment withdrawal occurred, treatment was discontinued and was resumed when the criteria for treatment resumption were satisfied. If adverse events meeting the criteria for dose reduction developed, the dose was reduced by one level before treatment was resumed.

Follow-up evaluations

After being allocated to the appropriate treatment group, the patients were followed-up for the evaluation of tumor control. We recorded local recurrence of the tumor, regional lymph node metastasis, and distant metastasis as local, regional, and distant failure, respectively. In patients with failed tumor control, we considered salvage surgery, radiotherapy, and/or additional chemotherapy. The survival after treatment was measured from the date of surgery to the date of death or last follow-up. The hematologic and non-hematologic toxicities of S-1 were prospectively scored according to the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 3.0.

Statistical analyses

The characteristics of the patients in the S-1 and SA groups were compared using Mann-Whitney's U and Fisher’s exact tests for categorical and continuous factors, respectively, for the overall cohort (OC). For the propensity score-matched cohort (PSMC), the Wilcoxon signed-rank test was used for continuous factors and the exact McNemar test or stratified conditional logistic regression analysis was used for categorical factors.

The primary endpoint was disease-free survival (DFS), defined as the time from the date of surgery to the date of confirmation of recurrence, delayed cervical lymph node metastasis, distant metastasis, or the diagnosis of secondary cancer or death from any cause, whichever occurred first. The secondary endpoints were OS and safety. OS was defined as the time from the date of surgery to the date of death from any cause. The time to relapse (TTR) was defined as the time from surgery to the diagnosis of local recurrence or cervical lymph node metastasis. The OS and DFS were calculated using the Kaplan-Meier method, and the difference between the two groups was analyzed using the log-rank test. The hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated by multivariate analyses, performed using the Cox proportional hazards regression model.

Prognostic and disease progression factors were considered for inclusion in the final models after calculating the coefficients and examining and ensuring that the proportion of missing data was below 25% [20]. All factors showing significance on univariate analysis were considered to fit the model. All factors with P < 0.2 were reviewed to avoid missing important factors and were then examined using multivariate analysis [21]. Two-sided probabilities were used, and P < 0.05 was considered statistically significant, unless otherwise noted. The propensity score was calculated using a binary logistic regression that included the patients’ characteristics. A propensity score, which reflected the probability of receiving S-1, was assigned to each patient. The S-1 and SA patients were randomly matched one-to-one, using greedy matching within propensity score calipers with no replacement [22]. The propensity scores were matched using a caliper width of 0.2 logits of the standard deviation to achieve a good covariate balance [22, 23]. The standardized differences were used to measure covariate balance, with an absolute standardized difference within 10% representing sufficient balance. The two matched subgroups were then analyzed for OS and DFS. Statistical analyses were performed using the Stata Statistical Software Program, Release 14.1 (StataCorp LP, College Station, TX, USA) and NCSS 10 Statistical Software Program (2015) (NCSS; LLC, Kaysville, UT, USA).

Results

Patient characteristics

From April 2004 to March 2012, a total of 95 cT2N0M0 OSCC patients were enrolled; 24 patients were assigned to the S-1 group and 71 to the SA group. The patient characteristics are summarized in Table 1. The only characteristic that significantly differed between the two groups was age (P < 0.001, Table 1).

Table 1

Patient characteristics in the overall cohort.

Characteristics		Surgery alone n (%)	S-1 adjuvant n (%)	P-value
	Total	71 (15.3)	24 (84.7)
Age (years)
Median	69	73	62	< 0.001	(a)
≤ 65	33	18 (54.5)	15 (45.5)	0.002	(b)
> 65	62	53 (85.5)	9 (14.5)
Sex
Male	53	39 (73.6)	14 (26.4)	0.816	(b)
Female	42	32 (76.2)	10 (23.8)
Oral subsite
Tongue	52	36 (69.2)	16 (30.8)	0.347	(b)
Maxilla	12	11 (91.3)	1 (8.3)
Mandible	22	18(81.8)	4 (18.2)
Oral floor	2	1 (50.0)	1 (50.0)
Buccal mucosa	7	5 (71.4)	2 (28.6)
Clinical phenotype
Superficial	41	32 (78.0)	9 (22.0)	0.519	(b)
Exophytic	23	15 (65.2)	8 (34.8)
Endophytic	31	24 (77.2)	7 (22.6)
Differentiation
Grade I	68	51 (75.0)	17 (25.0)	0.885	(b)
Grade II	25	18 (72.0)	7 (28.0)
Grade III	2	2 (100.0)	0 (0)
Mode of invasion
I, II	31	24 (77.4)	7 (22.6)	0.237	(b)
III	47	37 (78.7)	10 (21.3)
IVc, IVd	17	10 (58.8)	7 (41.2)
Local recurrence
No	83	62 (74.7)	21 (25.3)	> 0.999	(b)
Yes	12	9 (75.0)	3 (25.0)
Delayed cervical lymph node metastasis
No	79	57 (72.2)	22 (27.8)	0.343	(b)
Yes	16	14 (87.5)	2 (12.5)
Distant metastasis
No	92	69 (75.0)	23 (25.0)	0.384	(b)
Yes	3	2 (66.7)	1 (33.3)

(a) Mann-Whitney's U test for continuous factors and

(b) Fisher's exact test for categorical factors were used to calculate P-values between treatment options and clinicopathologic factors in 95 OSCC patients.

** indicated P < 0.01.

Abbreviations, OSCC, oral squamous cell carcinoma

Study treatments

The numbers of patients in the S-1 group who received the study treatment after 3, 6, and 12 months were 19 (79.2%), 17 (70.8%), and 14 (58.3%), respectively (Table 2). The reasons for discontinuing treatment in this group were the development of recurrence or metastasis in 2 (8.3%) patients and the physician’s judgement (mainly because of the occurrence of adverse events) in 8 (33.4%) patients.

Table 2

Treatment completion rates with S-1 adjuvant chemotherapy.

	S-1 (n = 24)
Duration	N	(%)
3 months	19	(79.2)
6 months	17	(70.8)
12 months	14	(58.3)

Adverse events

Table 3 shows the all-grade adverse events that occurred at an incidence rate of 4.2% (1 patient) or higher. An increase in the total bilirubin level was observed in 11 (45.8%) patients, anorexia was noted in 10 (41.7%) patients, anemia in 9 (37.5%) patients, fatigue and weight loss in 8 (33.3%) patients, thrombocytopenia in 7 (29.2%) patients, leukopenia, AST level increase and hyperpigmentation in 6 (25.0%) patients, rash/desquamation in 5 (20.8%) patients, ALT level increase in 4 (16.7%) patients, nausea in 3 (12.5%) patients, and vomiting in 2 (8.3%) patients. The following adverse events occurred at a severity of grade 3: anorexia in 2 (8.3%) patients and an increase in the total bilirubin level in 1 (4.2%) patient; they were in the S-1 group (Table 3). There were no treatment-related deaths in the S-1 group.

Table 3

Adverse events with S-1 adjuvant chemotherapy.

	S-1 (n = 24)
Adverse events	All grade		Garde 3+4
	n	(%)	n	(%)
Leukopenia	6	(25.0)	0	(0.0)
Neutropenia	1	(4.2)	0	(0.0)
Thrombocytopenia	7	(29.2)	0	(0.0)
Anemia	9	(37.5)	0	(0.0)
Total bilirubin increase	11	(45.8)	1	(4.2)
AST increase	6	(25.0)	0	(0.0)
ALT increase	4	(16.7)	0	(0.0)
Fatigue	8	(33.3)	0	(0.0)
Anorexia	10	(41.7)	2	(8.3)
Weight loss	8	(33.3)	0	(0.0)
Rash/desquamation	5	(20.8)	0	(0.0)
Hyperpigmentation	6	(25.0)	0	(0.0)
Diarrhea	1	(4.2)	0	(0.0)
Mucositis/Stomatitis	0	(0.0)	0	(0.0)
Nausea	3	(12.5)	0	(0.0)
Vomiting	2	(8.3)	0	(0.0)

Abbreviations: AST, aspartate transaminase and ALT, alanine transaminase

Survival analyses in the OC

In the OC, 71 patients received SA and 24 received S-1. Although there were no significant differences, the S-1 group showed a better TTR, DFS, and OS than the SA group (Figs 1, 2A and 2B). In particular, the DFS was better in the S-1 group (Fig 2A).

Fig 1

Cumulative hazard rate of the time to relapse in the overall cohort.

TTR, time to relapse; OC, overall cohort.

Fig 2

Cumulative survival curves of the S-1 adjuvant therapy (S-1 adjuvant) and surgery alone (surgery alone) groups in the overall cohort.

(A) Disease-free survival. (B) Overall survival. DFS, Disease-free survival; OS, overall survival; OC, overall cohort.

Survival analyses in the PSMC

In the PSMC, 20 patients each from the S-1 and SA groups were subjected to analysis after one-to-one propensity score matching (Table 4). As shown in Table 4, all baseline characteristics of patients in the PSMC were well-balanced (P ≥ 0.05). The TTR of the S-1 group was significantly lower than that of the SA group (P = 0.047). In the S-1 group, a significant improvement in prognoses was observed with respect to the DFS (P = 0.047), but not with respect to the OS (P = 0.073; Figs 3, 4A and 4B). Although there was no statistical significance, the proportion of patients with cervical lymph node metastasis in the S-1 group tended to be smaller than that in the SA group (Table 4).

Table 4

Patient characteristics in the propensity score-matched cohort.

Characteristics		Surgery alone n (%)	S-1 adjuvant n (%)	P—value
	Total	20 (50.0)	20 (50.0)
Age (years)
Median	64.0	64.0	64.0	0.674	(a)
≤ 65	22	11 (50.0)	11 (50.0)	> 0.999	(b)
> 65	18	9 (50.0)	9 (50.0)
Sex
Male	25	13 (52.0)	12 (48.0)	> 0.999	(b)
Female	15	7 (46.7)	8 (53.3)
Oral subsite
Tongue	23	10 (43.5)	13 (56.5)	0.573	(c)
Maxilla	3	2 (66.7)	1 (33.3)
Mandible	10	6 (60.0)	4 (40.0)
Oral floor	1	1 (100.0)	0 (0.0)
Buccal mucosa	3	1 (33.3)	2 (66.7)
Clinical phenotype
Superficial	16	8 (50.0)	8 (50.0)	0.698	(c)
Exophytic	10	4 (40.0)	6 (60.0)
Endophytic	14	8 (57.1)	6 (42.9)
Differentiation
Grade I	30	16 (53.3)	14 (46.7)	0.754	(b)
Grade II	10	4 (40.0)	6 (60.0)
Mode of invasion
I, II	13	6 (46.2)	7 (53.8)	0.517	(c)
III	19	12 (63.2)	7 (36.8)
IVc, IVd	8	2 (25.0)	6 (74.0)
Local recurrence
No	33	16 (48.5)	17 (51.5)	> 0.999	(b)
Yes	7	4 (57.1)	3 (42.9)
Delayed cervical lymph node metastasis
No	33	15 (45.5)	18 (54.5)	0.453	(b)
Yes	7	5 (71.4)	2 (28.6)
Distant metastasis
No	38	19 (50,0)	19 (50.0)	1.000	(b)
Yes	2	1 (50.0)	1 (50.0)

(a) Wilcoxon signed-rank test for continuous factors,

(b) Exact McNemar test for 2 x 2 categorical factors and

(c) Stratified conditional logistic regression for 2 x m categorical factors were used to calculate P-values between treatment options and clinicopathologic factors in 40 OSCC patients.

Fig 3

Cumulative hazard rate of the time to relapse in the propensity score-matched cohort.

PSMC, propensity score-matched cohort; TTR, time to relapse.

Fig 4

Cumulative survival curves of the S-1 adjuvant therapy (S-1 adjuvant) and surgery alone (surgery alone) groups in the propensity score-matched cohort.

(A) Disease-free survival. (B) Overall survival. DFS, Disease-free survival; OS, overall survival PSMC, propensity score-matched cohort.

Explanatory data analysis

In the OC, local recurrence developed in 9 patients in the SA group and 3 patients in the S-1 group. The HR was 1.249 (95% CI; 0.3377–4.616; Fig 5A). Delayed cervical lymph node metastasis developed in 14 patients in the SA group and 2 patients in the S-1 group. The HR was 2.809 (95% CI; 0.6377–12.38; Fig 5B). In the OC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups revealed that the HR for death was 4.271 (95% CI; 0.5411–32.680) in the SA group compared to the S-1 group (Fig 5C). In contrast, in the PSMC, local recurrence developed in 4 patients in the SA group and 3 patients in the S-1 group. The HR was 1.869 (95% CI; 0.4157–8.404; Fig 6A). Delayed cervical lymph node metastasis developed in 5 patients in the SA group and 2 patients in the S-1 group. The HR was 3.191 (95% CI; 0.6152–16.55; Fig 6B). In the PSMC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups indicated that the HR for death was 5.691 (95% CI; 0.6637–48.80) in the SA group compared to the S-1 group (Fig 6C).

Fig 5

Explanatory data analysis in overall cohort.

(A) Cumulative local recurrence rate of the S-1 adjuvant therapy (S-1 adjuvant) and surgery alone (surgery alone) groups. (B) Cumulative delayed cervical lymph node metastasis rate of the S-1 adjuvant therapy (S-1 adjuvant) and surgery alone (Surgery alone) groups. (C) Survival from loco-regional failures to death in patients with local recurrence/ delayed cervical lymph node metastasis.

Fig 6

Explanatory data analysis in the propensity score-matched cohort.

(A) Cumulative local recurrence rate of the S-1 adjuvant therapy (S-1 adjuvant) and surgery alone (surgery alone) groups. (B) Cumulative delayed cervical lymph node metastasis rate of the S-1 adjuvant therapy (S-1 adjuvant) and surgery alone (surgery alone) groups. (C) Survival from loco-regional failures to death in patients with local recurrence/ delayed cervical lymph node metastasis.

Discussion

This study was designed to evaluate the efficacy of adjuvant chemotherapy after curative surgery in patients with stage II OSCC. Tsukahara et al. recently reported convincing evidence for the benefits of adjuvant chemotherapy in patients with advanced head and neck cancer, who underwent curative therapy including surgery, radiotherapy, and chemoradiotherapy [13]. Therefore, we believe that investigating the effects of S-1 adjuvant chemotherapy in patients with early-stage OSCC may be valuable for establishing new treatment strategies. To the best of our knowledge, the present study is the first to indicate that adjuvant chemotherapy with S-1 improved the DFS in patients with stage II OSCC who received curative surgery for only the primary tumor compared to the DFS in a control group. Recently, Luryi et al. reported that in population-level data analyses, adjuvant chemotherapy is associated with compromised survival in patients with early-stage OSCC [24]. The study did not provide a detailed description of the chemotherapy regimens and included patients who underwent elective neck dissection; therefore, a detailed analysis of the differences in the results between this study and our study was not possible. However, it is necessary to understand the results of these studies and to interpret them carefully. The differences in the results may be related to the characteristic pharmacological action of S-1, as described below.

The treatment completion rate in the S-1 group was 58.3%. This rate was higher than the rate of 43.4% observed in a phase III study (ACTS-HNC) among patients with advanced HNSCC [13]. This difference may be attributed to the decrease in residual function in patients with advanced HNSCC, who underwent definitive therapy. In view of these findings, clinicians should carefully consider both, hematologic and non-hematological toxicities, and provide supportive therapy to prevent the discontinuation of S-1. However, the low incidence rates of grade 3 or higher grade adverse events in our study support the notion that S-1 administration may be an acceptable treatment option to further improve the prognoses of patients with stage II OSCC.

It is not clear why patient survival in the S-1 group was better than that in the SA group. Although there was no statistically significant difference between the groups, the present data, including the results of explanatory data analyses, showed that the cumulative rates of local recurrence and delayed cervical lymph node metastasis in the S-1 group tended to be smaller than those in the SA group in both the OC and PSMC. In addition, the time from recurrence or delayed cervical lymph node metastasis to death tended to be longer in the S-1 group. As observed in a previous study (ACTS-HNC) [13], these results possibly indicate that S-1 contributes to disease control after loco-regional failure in patients with OSCC. Among the various clinicopathological characteristics, local recurrence and/or regional lymph node metastasis have been proposed to be the prognostic indicators following surgery in patients with OSCC [25, 26]. Tumor angiogenesis is a hallmark of cancer; it is the essential process underlying tumor growth and progression, and, thereby, contributes to recurrence or metastasis. However, S-1 and its metabolites have been shown to suppress angiogenesis [27-29]. The anti-angiogenic effect of chemotherapy is known to be optimized through the metronomic administration of such drugs for prolonged periods [30]. Collectively, the survival benefit of S-1 administration in this study was probably attributable to both, the cytotoxic and anti-angiogenic activities.

Among early-stage OSCC patients, END has been shown to result in higher survival rates than therapeutic neck dissection [31]. However, END results in overtreatment in more than 70% of early OSCC patients and a high rate of complications [32]. In order to resolve these problems, sentinel lymph node biopsy (SLNB), which is less invasive and improves patients’ quality of life, has gained popularity in the treatment of patients with early-stage OSCC [33-36]. However, SLNB may not be universally applicable in routine medical practice. Therefore, in addition to SLNB, S-1 may warrant consideration as a therapeutic option in the cervical management of patients with early OSCC who undergo curative resection only for the primary tumor.

A limitation associated with our study is the small sample size; further studies with larger sample sizes are required to confirm the superiority of S-1 adjuvant chemotherapy over SA. In addition, comparative studies with other treatment options should be considered to confirm the superiority of S-1.

In conclusion, this retrospective study suggests that S-1 therapy was more effective than SA in the PSMC. We believe that S-1 adjuvant chemotherapy followed by curative surgery should be considered the standard of care in future phase III trials including patients with stage II (T2N0) OSCC.

20 Jan 2020

PONE-D-19-27210

Efficacy of adjuvant chemotherapy with S-1 in stage II oral squamous cell carcinoma patients: A comparative study using the propensity score matching method

PLOS ONE

Dear D.D.S.,PhD. Yoshida,

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ACADEMIC EDITOR:  Although the case number is too small, the RFS benefits are still noted. I suggest the authors validate the findings in an independent cohort soon. Of course, a phase III study would possibly change the current treatment guideline.  In addition, a 30% recurrence rate was observed in the first year after surgery (Figure 2.A), which seems too high. Please confirm that.

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Although the case number is too small, the RFS benefits are still noted. I suggest the authors validate the findings in an independent cohort soon. Of course, a phase III study would possibly change the current treatment guideline. In addition, a 30% recurrence rate was observed in the first year after surgery (Figure 2.A), which seems too high. Please confirm that.

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Reviewer #1: In the manuscript entitled ‘Efficacy of adjuvant chemotherapy with S-1 in stage II oral squamous cell carcinoma patients: A comparative study using the propensity score matching method’, Yoshida et al. evaluated the efficacy and safety of S-1 adjuvant chemotherapy compared with surgery alone in patients with stage II oral squamous cell carcinoma.

The effects of S1 adjuvent chemotherapy have been studied in multiple head and neck cancer types and in this regard, the current manuscript is incremental over our current knowledge of the effects of S1 adjuvent chemotherapy in SCC. To make the study suitable for publication in PLOS ONE, some qualitative and quantitative analysis of the lesions from follow up evaluations would be necessary. The authors mentioned that tumor local recurrence, regional lymph node metastasis, and distant metastasis as local, regional and distant failure were recorded. Some visual evidence in support of the same, along with graphical analysis would make the study more resourceful and suitable for publication in this journal.

In its current form, the study is more suitable for specialist clinical journals.

Reviewer #2: The authors have undertake a comparative study using the propensity score matching method for the efficacy of adjuvant chemotherapy with S-1 in stage II oral squamous cell carcinoma patients. The efficacy of adjuvant S-1 therapy In oral squamous cell carcinoma has not been reported yet, so this paper is very significant.

#1

In eligibility criteria, why creatine level ≥ 1.2 ?

#2

Is there any difference of surgical way between S1 and SA ? If so, you should consider the difference.

Reviewer #3: 1.The eligibility criteria in the study were patients with cT2N0 oral cancer, but cervical lymph node metastases were found in both the S-1 and the two groups of patients undergoing surgery alone (Table 1). It did not seem to meet the original eligibility criteria. Use of RT correlates with statistically significantly improved overall survival and cause-specific survival in patients with T2 disease. And the results did not specify the rate of neck lymph node dissection among patients undergoing surgery. In previous study, adjuvant RT significantly improves overall survival for patients with node-positive HNSCC. If these two groups of patients were node positive, adjuvant radiotherapy is required after surgery.

2. A large restrospective analysis have shown that adjuvant chemotherapy in patients with oral squamous cell carcinoma is associated with reduced survival(Luryi AL, et al. JAMA Otolaryngol Head Neck Surg. 2015. In current study showed that S-1 adjuvant chemotherapy maybe more efficient than surgery alone in early-stage OSCC patients. How to explain the differences between these finding.

3. In this retrospective study, the sample size of patients in the S-1 group was too small. Testing the efficacy of adjuvant chemotherapy with a limited number is statistically too ineffective.

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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19 Feb 2020

Responses to the Reviewers’ comments

Responses to Academic Editor

We sincerely appreciate the helpful comments from the reviewers, which have provided further insight and have helped considerably in improving the paper. As summarized below, we have revised the manuscript extensively, based on the reviewers’ comments. In the revised version of our paper, all of the changes are underlined and highlighted in yellow.

Comments: Although the case number is too small, the RFS benefits are still noted. I suggest the authors validate the findings in an independent cohort soon. Of course, a phase III study would possibly change the current treatment guideline. In addition, a 30% recurrence rate was observed in the first year after surgery (Figure 2.A), which seems too high. Please confirm that.

Comment 1: Although the case number is too small, the RFS benefits are still noted. I suggest the authors validate the findings in an independent cohort soon. Of course, a phase III study would possibly change the current treatment guideline.

Response to Comment 1:

We sincerely appreciate the pertinent observations and suggestions. However, owing to the limited duration of the study and the number of cases, we were unable to collect enough data for validation. We fully understand the need for validation; however, it was not feasible at present. We have added an exploratory analysis (Figures 5 and 6), based on the comments from other reviewers, and have revised the content of the Discussion section. We have added the following text in the Results section:

Page 13, line 220–Page 14, line 233

“Explanatory Data Analysis

In the OC, local recurrence developed in 9 patients in the SA group and 3 patients in the S-1 group. The HR was 1.249 (95% CI; 0.3377–4.616; Fig. 6A). Delayed cervical lymph node metastasis developed in 14 patients in the SA group and 2 patients in the S-1 group. The HR was 2.809 (95% CI; 0.6377–12.38; Fig. 6B). In the OC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups revealed that the HR for death was 4.271 (95% CI; 0.5411–32.680) in the SA group compared to the S-1 group (Fig. 5C). In contrast, in the PSMC, local recurrence developed in 4 patients in the SA group and 3 patients in the S-1 group. The HR was 1.869 (95% CI; 0.4157– 8.404; Fig. 6A). Delayed cervical lymph node metastasis developed in 5 patients in the SA group and 2 patients in the S-1 group. The HR was 3.191 (95% CI; 0.6152–16.55; Fig. 6B). In the PSMC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups indicated that the HR for death was 5.691 (95% CI; 0.6637–48.80) in the SA group compared to the S-1 group (Fig. 6C).”

We have made the following revisions in the Discussion section, as follows:

Page 15, lines 252- 261

“To the best of our knowledge, the present study is the first to indicate that adjuvant chemotherapy with S-1 improved the DFS in patients with stage II OSCC who received curative surgery for only the primary tumor compared to the DFS in a control group. Recently, Luryi et al. reported that in population-level data analyses, adjuvant chemotherapy is associated with compromised survival in patients with early-stage OSCC [24]. The study did not provide a detailed description of the chemotherapy regimens and included patients who underwent elective neck dissection; therefore, a detailed analysis of the differences in the results between this study and our study was not possible. However, it is necessary to understand the results of these studies and to interpret them carefully. The differences in the results may be related to the characteristic pharmacological action of S-1, as described below.”

Comment 2: In addition, a 30% recurrence rate was observed in the first year after surgery (Figure 2.A), which seems too high. Please confirm that.

Responses to Comment 2:

We had initially used the phrase “relapse-free survival", which was misleading to the readers. In this study, patients who underwent elective neck dissection were excluded, and patients with “relapse” included those with delayed cervical lymph node metastasis. The description “relapse” provided the impression that the incidence of local recurrence was approximately 30%; the description has accordingly been revised from “relapse-free survival” to “disease-free survival”. We also revised the terms “loco-regional recurrence” to “local recurrence” and “cervical lymph node metastasis” to “delayed cervical lymph node metastasis”. In our department, approximately 20% of the cT2N0 patients have delayed cervical lymph node metastasis after primary tumor resection; in view of the local recurrence rate, the loco-regional failure of 30% may be considered a reasonable value. Finally, we have revised the Materials and Methods section as follows:

Page 6, line 135–Page 7, line 137

“The primary endpoint was disease-free survival (DFS), defined as the time from the date of surgery to the date of confirmation of recurrence, delayed cervical lymph node metastasis, distant metastasis, or the diagnosis of secondary cancer or death from any cause, whichever occurred first.”

The following sentences were added in the Materials and Methods to clarify the eligibility criteria for this study:

Page 4, lines 79–82

“In our department, elective neck dissection is only performed for cases of N0 oral cancer for the purpose of reconstruction, and a “wait-and-see policy” has been adopted. Therefore, all patients enrolled in the present study only underwent resection of the primary tumor.”

Furthermore, the following text has been added in the Discussion section:

Page 17, lines 291–293

"Therefore, in addition to SLNB, S-1 may warrant consideration as a therapeutic option in the cervical management of patients with early OSCC who undergo curative resection only for the primary tumor. “

Responses to Reviewer 1:

We sincerely appreciate your helpful comments, which have provided further insight and have helped considerably in improving the paper. As summarized below, we have revised the manuscript extensively. In the revised version of our paper, all of the changes are underlined and highlighted in yellow.

Comments: The effects of S1 adjuvent chemotherapy have been studied in multiple head and neck cancer types and in this regard, the current manuscript is incremental over our current knowledge of the effects of S1 adjuvent chemotherapy in SCC. To make the study suitable for publication in PLOS ONE, some qualitative and quantitative analysis of the lesions from follow up evaluations would be necessary. The authors mentioned that tumor local recurrence, regional lymph node metastasis, and distant metastasis as local, regional and distant failure were recorded. Some visual evidence in support of the same, along with graphical analysis would make the study more resourceful and suitable for publication in this journal.

Response to Comments: We appreciate your pertinent observations and helpful suggestions. We have added the incidence of distant metastasis in Tables 1 and 4, have performed an exploratory analysis, and have added Figures 5 and 6 in the revised manuscript.

The following information has been added in the Results section

Page 13, line 220–Page 14, line 233

“Explanatory Data Analysis

In the OC, local recurrence developed in 9 patients in the SA group and 3 patients in the S-1 group. The HR was 1.249 (95% CI; 0.3377–4.616; Fig. 5A). Delayed cervical lymph node metastasis developed in 14 patients in the SA group and 2 patients in the S-1 group. The HR was 2.809 (95% CI; 0.6377–12.38; Fig. 5B). In the OC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups revealed that the HR for death was 4.271 (95% CI; 0.5411–32.680) in the SA group compared to the S-1 group (Fig. 5C). In contrast, in the PSMC, local recurrence developed in 4 patients in the SA group and 3 patients in the S-1 group. The HR was 1.869 (95% CI; 0.4157– 8.404; Fig. 6A). Delayed cervical lymph node metastasis developed in 5 patients in the SA group and 2 patients in the S-1 group. The HR was 3.191 (95% CI; 0.6152–16.55; Fig. 6B). In the PSMC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups indicated that the HR for death was 5.691 (95% CI; 0.6637–48.80) in the SA group compared to the S-1 group (Fig. 6C).”

The following text has been added in the Discussion section:

Page 16, lines 271–277

“Although there was no statistically significant difference between the groups, the present data, including the results of explanatory data analyses, showed that the cumulative rates of local recurrence and delayed cervical lymph node metastasis in the S-1 group tended to be smaller than those in the SA group in both the OC and PSMC. In addition, the time from recurrence or delayed cervical lymph node metastasis to death tended to be longer in the S-1 group. As observed in a previous study (ACTS-HNC) [13], these results possibly indicate that S-1 contributes to disease control after loco-regional failure in patients with OSCC.”

Responses to Reviewer 2:

Thank you for the valuable comments, which have provided further insight and have helped considerably in improving the paper. We have revised the manuscript extensively, as suggested. In the revised version of our paper, all of the changes are underlined and highlighted in yellow.

Comment #1: In eligibility criteria, why creatine level ≥ 1.2 ?

Response: As correctly observed, this part was incorrect. We have accordingly changed this to “creatinine level ≤ 1.2 mg/dL” in the revised manuscript (page 5, line 99).

Comment #2: Is there any difference of surgical way between S1 and SA ? If so, you should consider the difference.

Response: There was no difference in the surgical procedure between the SA and S-1 groups. We have added the following information in the Materials and Methods section for clarification:

Page 4, lines 79–82

“In our department, elective neck dissection is only performed for cases of N0 oral cancer for the purpose of reconstruction, and a “wait-and-see policy” has been adopted. Therefore, all patients enrolled in the present study only underwent resection of the primary tumor.”

Furthermore, the following text has been added in the Discussion section:

Page 17, lines 291–293

"Therefore, in addition to SLNB, S-1 may warrant consideration as a therapeutic option in the cervical management of patients with early OSCC who undergo curative resection only for the primary tumor. “

Responses to Reviewer 3:

We thank you for the helpful comments, which have provided further insight and have helped considerably in improving the paper. As summarized below, we have revised the manuscript extensively in accordance with your comments. In the revised version of our paper, all of the changes are underlined and highlighted in yellow.

Comment #1: The eligibility criteria in the study were patients with cT2N0 oral cancer, but cervical lymph node metastases were found in both the S-1 and the two groups of patients undergoing surgery alone (Table 1). It did not seem to meet the original eligibility criteria. Use of RT correlates with statistically significantly improved overall survival and cause-specific survival in patients with T2 disease. And the results did not specify the rate of neck lymph node dissection among patients undergoing surgery. In previous study, adjuvant RT significantly improves overall survival for patients with node-positive HNSCC. If these two groups of patients were node positive, adjuvant radiotherapy is required after surgery.

Response: We had initially used the phrase “cervical lymph node metastasis”, which was misleading for the readers. In our department, elective neck dissection is only performed for cases of N0 oral cancer for the purpose of reconstruction, and a “wait-and-see policy” has been adopted. Therefore, patients who underwent elective neck dissection were excluded from this study. To avoid confusion, we revised the term “cervical lymph node metastasis” to “delayed cervical lymph node metastasis”. The following information has been added in the Materials and Methods section to clarify the eligibility criteria for this study:

Page 4, line 79–82

“In our department, elective neck dissection is only performed for cases of N0 oral cancer for the purpose of reconstruction, and a “wait-and-see policy” has been adopted. Therefore, all patients enrolled in the present study only underwent resection of the primary tumor.”

Moreover, the following text has been added in the Discussion section:

Page 17, lines 291–293

"Therefore, in addition to SLNB, S-1 may warrant consideration as a therapeutic option in the cervical management of patients with early OSCC who undergo curative resection only for the primary tumor. “

Comment #2: A large restrospective analysis have shown that adjuvant chemotherapy in patients with oral squamous cell carcinoma is associated with reduced survival (Luryi AL, et al. JAMA Otolaryngol Head Neck Surg. 2015. In current study showed that S-1 adjuvant chemotherapy maybe more efficient than surgery alone in early-stage OSCC patients. How to explain the differences between these finding.

Response: As accurately observed, Luryi et al. recently reported that in population-level data analyses, adjuvant chemotherapy is associated with compromised survival in early-stage OSCC. The study does not provide a detailed description of the chemotherapy regimens and included patients who underwent elective neck dissection; therefore, it is not possible to analyze in detail why our results were contrary to those of Luryi et al. However, it is necessary to understand the results of such studies and to interpret them carefully. The difference may also be related to the characteristic pharmacological action of S-1. Therefore, we have added the following text in the Discussion section:

Page 15, lines 252-261

“To the best of our knowledge, the present study is the first to indicate that adjuvant chemotherapy with S-1 improved the DFS in patients with stage II OSCC who received curative surgery for only the primary tumor compared to the DFS in a control group. Recently, Luryi et al. reported that in population-level data analyses, adjuvant chemotherapy is associated with compromised survival in patients with early-stage OSCC [24]. The study did not provide a detailed description of the chemotherapy regimens and included patients who underwent elective neck dissection; therefore, a detailed analysis of the differences in the results between this study and our study was not possible. However, it is necessary to understand the results of these studies and to interpret them carefully. The differences in the results may be related to the characteristic pharmacological action of S-1, as described below.”

Comment #3: In this retrospective study, the sample size of patients in the S-1 group was too small. Testing the efficacy of adjuvant chemotherapy with a limited number is statistically too ineffective.

Response: We appreciate your concerns. However, owing to the limited duration of the study and the number of cases, we were unable to collect enough data. We fully understand that testing the efficacy of adjuvant chemotherapy with a limited number of cases is statistically ineffective. We had therefore, mentioned this as a limitation in the original manuscript as follows:

“A limitation associated with our study is the small sample size; further studies with larger sample sizes are required to confirm the superiority of S-1 adjuvant chemotherapy over SA.”

Nevertheless, we performed additional detailed analyses using current data. We have added the results of the exploratory analysis (Figures 5 and 6), in accordance with the comments from the other reviewers, and have revised the discussion accordingly. We have added the following information in the Results section:

Page 13, line 220–Page 14, line 233

“Explanatory Data Analysis

In the OC, local recurrence developed in 9 patients in the SA group and 3 patients in the S-1 group. The HR was 1.249 (95% CI; 0.3377–4.616; Fig. 6A). Delayed cervical lymph node metastasis developed in 14 patients in the SA group and 2 patients in the S-1 group. The HR was 2.809 (95% CI; 0.6377–12.38; Fig. 6B). In the OC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups revealed that the HR for death was 4.271 (95% CI; 0.5411–32.680) in the SA group compared to the S-1 group (Fig. 5C). In contrast, in the PSMC, local recurrence developed in 4 patients in the SA group and 3 patients in the S-1 group. The HR was 1.869 (95% CI; 0.4157– 8.404; Fig. 6A). Delayed cervical lymph node metastasis developed in 5 patients in the SA group and 2 patients in the S-1 group. The HR was 3.191 (95% CI; 0.6152–16.55; Fig. 6B). In the PSMC, comparison of the survival time from local recurrence or delayed cervical lymph node metastasis between the treatment groups indicated that the HR for death was 5.691 (95% CI; 0.6637–48.80) in the SA group compared to the S-1 group (Fig. 6C).”

We have also added the following text in the Discussion section:

Page 16, lines 271–277

“Although there was no statistically significant difference between the groups, the present data, including the results of explanatory data analyses, showed that the cumulative rates of local recurrence and delayed cervical lymph node metastasis in the S-1 group tended to be smaller than those in the SA group in both the OC and PSMC. In addition, the time from recurrence or delayed cervical lymph node metastasis to death tended to be longer in the S-1 group. As observed in a previous study (ACTS-HNC) [13], these results possibly indicate that S-1 contributes to disease control after loco-regional failure in patients with OSCC.”

We thank you again for your helpful suggestions, and hope that you will now find the revised manuscript suitable for publication.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

30 Mar 2020

Efficacy of adjuvant chemotherapy with S-1 in stage II oral squamous cell carcinoma patients: A comparative study using the propensity score matching method

PONE-D-19-27210R1

Dear Dr. Yoshida,

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All of the questions were answered adequately.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

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Reviewer #2: Yes

Reviewer #3: Partly

**********

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Reviewer #2: Yes

Reviewer #3: Yes

**********

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Reviewer #2: Yes

Reviewer #3: Yes

**********

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Reviewer #3: Yes

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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 #2: The manuscript was significantly improved. The authors addressed most of my concerns. This manuscript is suitable for PLOS ONE.

Reviewer #3: The author has extensively revised the manuscript.

Some additional exploratory analysis may contribute to the limitations of few samples and short following time

**********

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Reviewer #2: No

Reviewer #3: No

1 Apr 2020

PONE-D-19-27210R1

Efficacy of adjuvant chemotherapy with S-1 in stage II oral squamous cell carcinoma patients: A comparative study using the propensity score matching method

Dear Dr. Yoshida:

I am 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.

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