Categorization of Breast Fine Needle Aspirates Using the International Academy of Cytology Yokohama System Along with Assessment of Risk of Malignancy and Diagnostic Accuracy in a Tertiary Care Centre.

CONTEXT: The International Academy of Cytology Yokohama System has developed a standardized system of reporting breast cytology by classifying them into five categories - insufficient, benign, atypical, suspicious, and malignant. Numerous studies conducted at different centers are required to confirm the risk of malignancy of the different categories. AIMS: The main objectives of our study were to classify breast fine needle aspirates according to the IAC Yokohama system and assess the risk of malignancy, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy. SETTINGS AND
DESIGN: It was a retrospective study done over a period of 2 years from January 2018 to December 2020.
MATERIALS AND METHODS: All breast FNAs done in the above period were retrieved and classified into five categories according to the Yokohama system. Histopathological diagnosis was also retrieved wherever available. STATISTICAL ANALYSIS USED: Using a histopathological diagnosis as the gold standard, sensitivity, specificity, PPV, NPV, and diagnostic accuracy were calculated. For each of the five categories, the risk of malignancy was also assessed.
RESULTS: Out of the 554 breast fine needle aspirates, 242 had histopathological correlation. The risk of malignancy for insufficient, benign, atypical, suspicious, and malignant categories were 5%, 1.5%, 17.4%, 81.8%, and 100%, respectively. Maximum sensitivity (97.2%) was achieved when atypical, suspicious, and malignant cases were considered as positive test results. The highest specificity (100%) was observed when only malignant cases were considered as positive test results, whereas maximum diagnostic accuracy (96.4%) was noted when the malignant and suspicious category was included in positive test results.
CONCLUSION: The IAC Yokohama system is an excellent system for accurately diagnosing breast fine needle aspirates with greater reproducibility of reports and better communication between the pathologist and clinician. Copyright:

INTRODUCTION

Breast carcinoma is the most common cancer in females worldwide. It is the most common cause of cancer-related deaths in women in developing countries. In developed nations, it is the second cause of cancer-related deaths subsequent to lung cancer.[1]

In India, the incidence rate is as high as 26 per 1,00,000 women population, whereas mortality rate is 13 per 1,00,000 women population.[2]

Fine needle aspirate is a simple, rapid, cost-effective, and minimally invasive test for both palpable and impalpable (under ultrasonographic guidance) breast lumps. However, nowadays usage of core needle biopsy has gained popularity as it allows evaluation of histological grade as well as hormonal status [estrogen receptor (ER)/ progesterone receptor(PR)/human epidermal growth factor receptor (Her2)].

For the diagnosis of breast cancer, FNAC has a high sensitivity of 90%–95% and a high positive predictive value ~100%.[3]

It has a low false-negative rate related to low-grade ductal and lobular carcinoma and a very low false-positive rate related to FNAs of fibroadenomas and papillary lesions of the breast.[456]

Using ultrasonography (USG) guidance and rapid on-site evaluation (ROSE) optimizes the usage of FNAC. The cytological findings should be interpreted along with clinical and radiological findings in the “triple test.” With the triple test parameters, the sensitivity and specificity of FNAC is comparable to core needle biopsy.[5]

The IAC Yokohama Breast FNAC Reporting system has been developed by a group of expert cytopathologists with assistance from surgeons, oncologists, and radiologists. It has been developed to have a standardized reporting system to improve the interpretation of breast cytology. It also aims at improving communication between the cytopathologist and clinician by linking reporting system with management options.[7]

The present study aims at classifying the breast FNAs according to the IAC Yokohama system and evaluating the risk of malignancy and diagnostic accuracy of different categories. The sensitivity, specificity, PPV, and NPV were also assessed.

MATERIALS AND METHODS

It was a retrospective study in which all the breast fine needle aspirates done from January 2018 to December 2020 were retrieved (554 FNAs corresponding to 537 cases) after approval from the institutional ethics committee. Informed consent was taken from all patients before FNAC. At least two passes were done from each breast lump, and the adequacy of smears was assessed using rapid onsite evaluation with Toluidine blue stain. For breast lesions that were radiologically nonfibrotic and solid, adequacy criteria of at least seven cellular fragments with at least 20 cells in each fragment was suggested, provided no atypical/suspicious or malignant cells were identified. The final reporting was done on smears stained with May Grunwald Giemsa and Papanicolaou stains.

The clinical details were also retrieved, and all cases were categorized according to the IAC Yokohama reporting system into five categories –

C1. Insufficient

C2. Benign

C3. Atypical

C4. Suspicious of Malignancy

C5. Malignant.

Histological diagnosis, which was considered the gold standard, was available in 242 cases (45.1%).

Statistical analysis

The risk of malignancy (ROM) was calculated for each category as the number of malignant cases confirmed histologically/total number of cases in the diagnostic category. The cases in the insufficient category were excluded from further statistical analysis, as they could not be included in either negative or positive for malignancy. Using the histological diagnosis as the gold standard, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated.

Sensitivity = True positive/(True positive + False negative)

Specificity = True negative/(True negative + False positive)

PPV = True positive/(True positive + False positive)

NPV = True negative/(True negative + False negative)

Diagnostic accuracy = (True positive + True negative)/All analyzed cases

The above ratios were calculated for the following groups–

Group A- Only the “malignant” category was regarded as a positive report.

Group B- All cases in the “malignant” and “suspicious of malignancy” category were regarded as positive for malignancy.

Group C- All cases in the “malignant,” “suspicious of malignancy,” and “atypical” categories were regarded as positive for malignancy.

RESULTS

A total of 537 patients underwent 554 breast fine needle aspirates in the period from January 2018 to December 2020. The age group of patients ranged from 15 years to 79 years with the majority of cases belonging to the 3rd and 4th decades. Bilateral lesions were seen in 17 (3.2%) cases, whereas the remaining had unilateral lesions.

The 554 breast FNAs were categorized according to the IAC Yokohama System as follows:

C1. Insufficient- 20 cases (3.6%)

C2. Benign- 385 cases (69.5%)

C3. Atypical- 35 cases (6.3%)

C4. Suspicious of malignancy- 13 cases (2.3%)

C5. Malignant- 101 cases (18.2%).

Histopathological correlation was available in 242 cases (45.1%). The histopathological diagnoses for the breast lesions in different cytological categories were evaluated and are summarized with cyto- histological correlation in Table 1.

Table 1

Distribution of IAC Yokohama System categories with cyto- histological correlation and Risk of malignancy

	Insufficient	Benign	Atypical	Suspicious of Malignancy	Malignant
Histological Benign diagnosis	19 (Fibrocystic disease-7, Inflammatory lesion-2, Gynaecomastia-2, Benign pyllodes-3, Fibroadenoma- 5)	129 (Fibroadenoma- 88, Abscess- 12, Galactocele- 6, Granulomatous mastitis- 2, Fibrocystic disease- 12, Fat necrosis- 2, Gynecomastia- 7)	19 (Cellular FA- 6, Benign phyllodes- 7, Benign papillary lesion- 2, Fibroadenoma with usual ductal hyperplasia- 4)	2 (Cellular FA- 2)	0
Histological Malignant diagnosis	1 (Invasive ductal carcinoma- 1)	2 (DCIS- 1, Invasive ductal carcinoma- 1)	4 (Invasive ductal carcinoma- 3, Papillary DCIS- 1)	9 (Invasive ductal carcinoma- 7, DCIS- 2)	57 (DCIS- 2, Invasive ductal carcinoma- 50, Invasive lobular carcinoma- 5)
Risk of Malignancy	5%	1.5%	17.4%	81.8%	100%

The ROM for insufficient, benign, atypical, suspicious, and malignant categories were 5%, 1.5%, 17.4%, 81.8%, and 100%, respectively. The sensitivity, specificity, PPV, NPV, and diagnostic accuracy of the three groups are summarized in Table 2.

Table 2

Sensitivity, specificity, PPV, NPV, accuracy of IAC Yokohama System

	Group A (Category Malignant considered positive)	Group B (Category Malignant and Suspicious considered positive)	Group C (Category Malignant, Suspicious, and Atypical considered positive)
Sensitivity	79.2%	91.7%	97.2%
Specificity	100%	98.7%	86.0%
PPV	100%	97.1%	77.0%
NPV	90.9%	96.1%	98.5%
Accuracy	93.2%	96.4%	89.6%

Maximum diagnostic accuracy is achieved (96.4%) when malignant and suspicious of malignancy are considered positive, whereas highest sensitivity is achieved (97.2%) when malignant, suspicious, and atypical are considered positive for malignancy.

Among the suspicious and malignant categories, invasive ductal carcinoma was the most common histological diagnosis, whereas in the benign category, fibroadenoma was the most common. In the atypical category, the majority (82.6%) of the histological diagnoses were benign (cellular fibroadenomas and benign phyllodes).

DISCUSSION

All breast lesions should be evaluated by “triple test” approach, which combines clinical, radiological, and pathological parameters to arrive at a final diagnosis and guide patient management. Classically, the triple test includes clinical examination, mammography, and FNAC. However, in the present scenario, it also includes USG, especially in the context of young women and core needle biopsy as an alternative to FNAC.[8]

Despite FNAC being a simple and cost-effective procedure with a short turnaround time, usage of core needle biopsy has gained popularity as it allows the assessment of histological grade and hormonal status. When used in concordance with clinical and radiological findings, the sensitivity and specificity of FNAC is comparable to that of core needle biopsy.[5] FNAC can also be used to assess ER/PR/Her2 status through immunohistochemistry on cell blocks as is done in our tertiary center.

FNAC has a very crucial role to play, especially in a tertiary care center like ours where it is not feasible to take an adequate number of core needle biopsies in each patient with a breast lump due to time and cost limitations. Moreover, it is easier to perform in experienced hands and more cost-effective as compared to core needle biopsies. Despite it being a rapid test, turnaround time can be further reduced using rapid on-site evaluation. In addition, FNAC is also a more suitable procedure for breast lesions close to the chest wall/vessels or in patients on anticoagulants.[9] In our center, we preferably use FNA for evaluation of breast lumps except in cases of atypical or suspicious categories where it is followed up by a core needle biopsy for confirmation.

The use of a standardized reporting system will aid in the reproducibility of reports between different institutions and better patient care through improved communication between clinicians and pathologists.[7]

In the present study, 554 fine-needle aspirates from the breast were retrospectively categorized according to the IAC Yokohama Reporting System. Our study had 3.6% insufficient, 69.5% benign, 6.3% atypical, 2.3% suspicious, and 18.2% malignant lesions, respectively. This distribution is similar to the results obtained by Kamatar et al.[10] who had 5% C1, 71% C2, 1% C3, 2% C4, and 21% C5 lesions, respectively [Table 3].

Table 3

Distribution of breast lesions according to IAC Yokohama System in various published studies

	Insufficient	Benign	Atypical	Suspicious of Malignancy	Malignant
De Rosa et al.[11] (n=4624)	19.2%	36.9%	10.8%	4.7%	28.4%
Mc Hugh et al.[12] (n=695)	9%	47%	7%	11%	26%
Wong et al.[5] (n=2696)	11.2%	72%	4.3%	2.2%	10.3%
Montezuma et al.[6] (n=3625)	5.77%	73.38%	13.74%	1.57%	5.54%
Agarwal et al.[9] (n=1205)	19%	50.2%	6.6%	3.8%	20.4%
Kamatar et al.[10] (n=470)	5%	71%	1%	2%	21%
Apuroopa et al.[13] (n=900)	4.3%	58%	17.7%	7.2%	12.8%
Present study (n=554)	3.6%	69.5%	6.3%	2.3%	18.2%

The ROM for various categories in the present study was 5% for C1, 1.5% for C2, 17.4% for C3, 81.8% for C4, and 100% for C5. These results are in concordance with the studies by Wong et al.[5] Montezuma et al.,[6] and Apuroopa et al.[13] [Table 4].

Table 4

Risk of malignancy of different categories of IAC Yokohama System in various published studies

	Insufficient	Benign	Atypical	Suspicious of Malignancy	Malignant
De Rosa et al.[11]	49.6%	4.9%	20.7%	78.7%	98.8%
Mc Hugh et al.[12]	0%	12%	25%	46%	91%
Wong et al.[5]	2.6%	1.7%	15.7%	84.6%	99.5%
Montezuma et al.[6]	4.8%	1.4%	13%	97.1%	100%
Agarwal et al.[9]	60.9%	8.3%	17.2%	77.8%	100%
Kamatar et al.[10]	0%	4%	66%	83%	99%
Apuroopa et al.[13]	5%	1.2%	12.5%	93.65%	100%
Present study	5%	1.5%	17.4%	81.8%	100%

In the current study, the maximum sensitivity (97.2%) was achieved when atypical, suspicious, and malignant cases (Group C) were considered positive test results. However, the inclusion of atypical cases in positive results resulted in decreased specificity and accuracy. The highest specificity (100%) was seen when only malignant cases (Group A) were included in positive test results, whereas maximum diagnostic accuracy (96.4%) was observed when malignant and suspicious (Group B) cases were included in positive results. Wong et al.[5] Montezuma et al.[6] Agarwal et al.,[9] and De Rosa et al.[11] demonstrated similar findings. McHugh et al.[12] observed highest sensitivity and specificity in similar scenarios, but they observed maximum accuracy when only malignant cases were considered as positive test results [Table 5].

Table 5

Comparison of diagnostic accuracy of breast FNAC in diagnosis of malignancy using Yokohama system in various studies

Category included		De Rosa et al.[11]	McHugh et al.[12]	Wong et al.[5]	Montezuma et al.[6]	Agarwal et al.[9]	Present study
	No. of cases	1616	199	536	755	299	224
Only malignant category taken as positive	Sensitivity	82.2%	65.4%	75.4%	68.7%	86.7%	79.2%
	Specificity	97.8%	95.9%	100%	100%	100%	100%
	PPV	98.8%	91.1%	100%	100%	100%	100%
	NPV	71.0%	81.1%	80.7%	87.7%	71.2%	90.9%
	Accuracy	87.0%	83.9%	87.9%	90.3%	90.0%	93.2%
Suspicious of malignancy and malignant taken as positive	Sensitivity	93.7%	79.5%	92.0%`	83.3%	96.0%	91.7%
	Specificity	90.8%	85.1%	97.8%	99.8%	91.9%	98.7%
	PPV	95.8%	77.5%	97.6%	99.5%	97.3%	97.1%
	NPV	86.6%	86.6%	92.7%	93.0%	88.3%	96.1%
	Accuracy	92.8%	82.9%	95.0%	94.7%	95.0%	96.4%
Atypical, suspicious and malignant category taken as positive	Sensitivity	98.9%	84.6%	98.9%	98.3%	98.2%	97.2%
	Specificity	46.3%	75.2%	62.1%	54.8%	59.5%	86.0%
	PPV	80.5%	68.8%	71.7%	49.2%	88.0%	77.0%
	NPV	95.1%	88.3%	98.3%	98.6%	91.7%	98.5%
	Accuracy	82.7%	78.9%	80.2%	68.2%	88.6%	89.6%

Most of the breast lesions included in the atypical category were either cellular fibroadenomas or low-grade phyllodes on histology. Both of these lesions are difficult to differentiate on cytomorphology. The presence of loose cohesive clusters with mild atypia and very few benign bipolar nuclei in the background led to the categorization of a fibroadenoma with focal usual ductal hyperplasia as proliferative breast disease with atypia [Figure 1]. The scarcity of myoepithelial cells and mild epithelial atypia prevented us from giving a benign diagnosis in the two cases of cellular fibroadenomas included in the suspicious category. Misdiagnosis of malignant lesions as benign/atypical resulted from scant cellularity associated with low-grade atypia. Two cases of invasive ductal carcinoma were wrongly categorized as atypical due to being deep-seated lesions leading to hypocellular smears with few atypical cells. Another case of invasive ductal carcinoma with ductal carcinoma in situ was mislabeled as a proliferative disease with atypia due to des cohesive clusters with low nuclear grade and very few ductal cells exhibiting significant nuclear enlargement [Figure 2].

Figure 1

(a, b) Loose cohesive clusters with mild nuclear enlargement and few benign bipolar nuclei in the background reported as Proliferative breast disease with atypia – Category 3 (400 ×, May Grunwald Giemsa) (c, d) Histological diagnosis was a fibroadenoma with focal usual ductal hyperplasia (200 ×, Hematoxylin and eosin)

Figure 2

(a, b) Discohesive clusters with moderate nuclear enlargement with a paucity of myoepithelial cells in the clusters reported as Category 3 (400 ×, May Grunwald Giemsa). (c, d) Histological diagnosis turned out to be invasive ductal carcinoma with the focus of Ductal carcinoma in-situ (100 ×, 200 ×, respectively, Hematoxylin and eosin)

The two malignant lesions, which were reported as benign were possibly due to sampling error. Thus, whenever two out of three “triple test” parameters show discordant findings, it should be followed up by a core needle biopsy.[14] The two indeterminate categories in the Yokohama System – atypical and suspicious – allow for the classification of borderline lesions like atypical ductal hyperplasia, which carry a greater risk of developing malignancy than benign lesions.[9]

The IAC Yokohama Reporting System for breast cytology provides a uniform reporting platform with better reproducibility of reports similar to the Milan system of reporting salivary gland lesions and the Bethesda system for reporting thyroid cytopathology. The ROM of different categories are similar to the ROMs suggested in the original publication of the Yokohama system. We recommend the usage of FNA for the evaluation of breast lumps and further categorization based on the Yokohama system. The core needle biopsy can be limited only in cases where the cytological diagnosis is atypical, suspicious, or malignant.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.