The accurate and timely diagnosis of breast lesions is paramount in clinical practice, guiding patient management and improving prognostic outcomes. For many years, fine needle aspiration cytology (FNAC) has served as an indispensable, minimally invasive, and cost-effective tool in the initial evaluation and early detection of these lesions. Its ability to provide rapid cellular diagnoses has made it a cornerstone in breast pathology1.

However, the inherent morphological heterogeneity and diagnostic challenges posed by various breast pathologies necessitate a highly standardized and consistent approach to cytological interpretation2,3. Variability in reporting criteria can lead to discrepancies, potentially affecting patient care. To address this critical need for uniformity, the Yokohama classification system for breast cytology was developed in 2016, this internationally recognized system provides a structured framework, categorizing breast cytology findings into five distinct diagnostic groups4. Therefore, this study was undertaken to classify breast lesions according to the Yokohama classification system and to evaluate its diagnostic accuracy.

Objectives -

1. To categorize breast fine needle aspiration cytology (FNAC) lesions according to the Yokohama classification system.
2. To assess the diagnostic accuracy of the Yokohama classification by correlating cytological diagnoses with subsequent histopathological findings.

This is a retrospective study spanning for a one-year period. The study was carried out within the Department of Pathology at Belagavi Institute of Medical Sciences, Belagavi, Karnataka. All available cytology slides pertaining to breast fine needle aspirations performed during the study period were retrieved from the departmental archives. Each retrieved slide was then meticulously re-evaluated and classified according to the established criteria of the Yokohama classification system(Table 1). 1-4

To ascertain diagnostic accuracy, histopathological correlation was performed for all cases where corresponding biopsy or surgical excision specimens were available. The histopathological diagnoses served as the gold standard against which the Yokohama cytological classifications were compared. Cases without available histopathological follow-up were included in the overall cytologic classification analysis but excluded from the diagnostic accuracy calculations.

Statistical Analysis

All collected data were compiled and subjected to statistical analysis using SPSS software (Statistical Package for the Social Sciences), version 29. The primary focus of the statistical analysis was to determine various parameters of diagnostic accuracy, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall diagnostic accuracy, for the Yokohama classification system.

The development of the Yokohama classification stemmed from a global recognition of the need for a universally accepted terminology in breast cytopathology. Prior to its inception, a variety of institutional and regional reporting schemes existed, often leading to inconsistencies in diagnosis and communication between cytopathologists and clinicians. This lack of standardization hindered appropriate patient management^1-4.

Recognizing this critical gap, the International Academy of Cytology (IAC) initiated a collaborative effort involving a diverse group of expert cytopathologists, radiologists, surgeons, and oncologists from around the world. This concerted endeavor culminated in a pivotal meeting in Yokohama, Japan, in 2016, where the consensus-driven system was formally established. The primary goals were to create a uniform lexicon, define clear diagnostic criteria for each category, provide associated risks of malignancy (ROM), and suggest management algorithms^1-4.

In the present study, comparison of FNAC case distributions across various studies reveals a slight variability in the most commonly affected age group. Consistent with findings from Sreedevi CH et al.² and Raj et al.³, the present study observed the highest incidence of breast lesions in the 21–30 years age group. Conversely, other significant studies by Badge SA et al.⁴ and Sunitha et al.⁶ reported a greater prevalence in the subsequent 31–40 years age group. Notably, the current study identified a strong concentration of cases (74%) within the 21–30 years demographic, indicating a pronounced younger age predominance in our cohort. The significant representation of younger individuals in our study population particularly emphasizes the critical importance of promoting early awareness and implementing targeted screening initiatives, especially women in their third decade of life^7,8,9. This understanding is vital for public health planning and educational campaigns aimed at timely detection and intervention (Table 8).

In the current study, the comparison of FNAC cases according to laterality across various studies reveals no consistent dominance of either breast. While studies by Sreedevi CH et al.² and Gore et al.⁷ report a higher incidence in the right breast, studies by Nigam et al.⁸, Raj et al.³ and the present study show a predominance of cases in the left breast. In the present study, 50% of cases involved the left breast, indicating a slight left-sided predominance. Overall, the data suggest a nearly balanced distribution, with minimal clinical significance attributed to laterality^10,11 (Table 9).

The distribution of breast lesions classified by the International Academy of Cytology (IAC) Yokohama system in the present study demonstrates patterns consistent with much of the contemporary literature^1-10 (Table 10). Our findings, which show a predominance of Category C2 (benign) lesions followed by C3 (atypical), align closely with the observations reported by Montezuma et al.⁹ Similar trends, where C2 remains the most frequently reported category, have been consistently noted across various other studies, including those by Dogra A et al.¹⁰, Nigam JS et al.⁸, and Kamatar et al.¹¹ This consistent prevalence of C2 lesions across diverse studies reinforces the fundamental understanding that benign conditions constitute the vast majority of breast lesions encountered in cytology practice^8-10. Furthermore, this broad alignment underscores the value and effectiveness of the Yokohama system in providing a standardized, clear and globally applicable framework for breast cytology reporting^11-13.

               *PPV- Positive predictive valu

             **NPV- Negative predictive value

Comparing the diagnostic reliability of the Yokohama classification for breast lesions across various studies reveals a consistent pattern of high sensitivity, specificity, and overall diagnostic accuracy, reaffirming its effectiveness in cytodiagnosis (Table 11). Our present study reported a sensitivity of 100% and a Negative Predictive Value (NPV) of 100%, aligning closely with the high NPVs observed by Montezuma et al.9 (98.62%) and Kamatar et al.11 (98%). This highlights the Yokohama system's strong capability to accurately identify all malignant cases and reliably rule out malignancy11-15.

While our study's specificity of 90.27% indicates a strong ability to correctly identify truly benign lesions, this shows slight variation when compared to other studies like Montezuma et al.9, Malvina D. & Reshma G.12, and Dogra A. et al.10 reported a perfect 100% specificity. This difference in specificity might reflect variations in patient populations. Nevertheless, a specificity exceeding 90% still strongly supports the Yokohama system's effectiveness in accurately classifying benign cases and minimizing false-positive diagnoses, which is crucial for preventing unnecessary anxiety and invasive procedures for patients15-18.

A notable difference lies in our Positive Predictive Value (PPV) of 56.25%, which is considerably lower than the 100% reported in several other studies8-15. This suggests that while the reporting system is highly sensitive, there might be a higher rate of false positives as in our study. The morphological overlap between benign proliferative lesions such as atypical ductal hyperplasia or fibroadenoma with prominent atypia and true malignancies can pose diagnostic challenges, leading to an over-diagnosis11-15. Additionally, sampling limitations during the FNA procedure might yield a cytological specimen that is not fully representative of the entire lesion, potentially capturing atypical benign cells in isolation without the broader context that a histopathological biopsy would provide15-18. Despite this, the overall diagnostic accuracy of 91.35% in our study remains comparable to or even exceeds that of Dogra A. et al.10 (90%), and is only slightly less than Kamatar et al.11 (95%), Malvina D. & Reshma G.12 (96.82%), and Montezuma et al.9 (99.11%). This overall consistency across studies, despite variations in individual metrics, strongly reinforces the Yokohama classification as a reliable and standardized tool for the cytological evaluation of breast lesions.

The present study's findings, particularly the observed overall diagnostic accuracy of 91.35%, strongly exemplify the pivotal advancement offered by the International Academy of Cytology (IAC) Yokohama classification system in breast FNAC reporting. This system provides a much-needed systematic and standardized approach to cytological evaluation. The successful adoption of the Yokohama classification in routine diagnostic practice represents a significant stride towards achieving excellence in breast cytology. It demonstrably improves both the clarity and reliability of cytological diagnoses, which are critical for enhancing inter-pathologist consistency and optimizing communication with clinicians. Ultimately, this enhanced precision in reporting directly contributes to improved patient stratification and better-informed management decisions, thereby elevating the standard of care for individuals with breast lesions.

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