Abstract

Background: Breast lumps require prompt and reliable assessment because malignant lesions may be clinically indistinguishable from benign conditions at presentation. Fine-needle aspiration cytology (FNAC) remains a practical first-line investigation in many hospitals because it is quick, inexpensive and minimally invasive. The International Academy of Cytology (IAC) Yokohama reporting system groups breast FNAC findings into five diagnostic categories linked to an estimated risk of malignancy (ROM). Rapid on-site evaluation (ROSE) can additionally confirm whether aspirated material is adequate before the patient leaves the procedure area. Objective: To determine the diagnostic performance of the IAC Yokohama system for breast FNAC at three cytological positivity thresholds. Additional objectives were to describe the distribution of cases within the five Yokohama categories, estimate the ROM for each category and examine the usefulness of ROSE in prospective samples. Methods: This cross-sectional analytical study was undertaken in the Department of Pathology, JSS Medical College, Mysore, over 42 months. A total of 180 patients with palpable breast lumps and available cytological and histopathological diagnoses were studied. The dataset included 86 retrospective cases and 94 prospective cases. In the prospective arm, FNAC was performed using aseptic precautions and smear adequacy was checked on site with toluidine blue staining. Each cytology specimen was assigned to category C1, C2, C3, C4 or C5 according to the IAC Yokohama system. Histopathology was treated as the reference standard. Diagnostic indices were calculated for three positive-test definitions: C5 alone; C4 plus C5; and C3 plus C4 plus C5. Results: Of the 180 aspirates, 8 (4.4%) were categorized as C1, 106 (58.9%) as C2, 14 (7.8%) as C3, 2 (1.1%) as C4 and 50 (27.8%) as C5. The category-wise ROM was 25% for C1, 0.94% for C2, 35.7% for C3, 100% for C4 and 98% for C5. The most inclusive threshold (C3-C5 positive) yielded the greatest sensitivity (98.3%), whereas the C5- only and C4-C5 thresholds both showed a specificity of 99.1%. The best overall diagnostic accuracy was obtained when C4 and C5 were regarded as positive (95.3%). Among cases assessed with ROSE, inadequate smears accounted for 3.2%. Conclusion: Classification of breast FNAC using the IAC Yokohama system produced clinically meaningful ROM estimates and showed strong agreement with histopathology, especially for benign and malignant categories. A positivity threshold that included suspicious and malignant aspirates provided the most balanced diagnostic performance. ROSE was associated with a low proportion of inadequate samples in the prospective component and may improve the efficiency of FNAC-based evaluation.

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