FNA of breast fibroadenoma: observer variability and review of cytomorphology with cytohistological correlation

OBJECTIVE: To determine the observer variability in reporting fibroadenoma of the breast by fine needle aspiration (FNA) and to review the cytomorphological features of the lesion with cytohistological correlation. METHODS: Retrospective analysis of FNA smears from 110 cases diagnosed as fibroadenoma of which surgical pathology follow-up was available in 33. Two pathologists were asked to categorize smears from 67 cases of breast lesions while blinded to the clinical finding as fibroadenoma, epithelial hyperplasia (usual and atypical) and malignant. All fibroadenoma (33) and cancer (15) cases were biopsy-proven. The same set of slides was re-circulated to one of the pathologists, and his first and second round results were compared. RESULTS: Pre-review cytohistological correlation was attained in 32 of 33 cases of fibroadenoma (97%). The overall agreement between the two observers was 87% Kappa = 0.74, 95% confidence interval (CI) 0.72-0.76]. Cytohistological correlation was achieved in 26 of 33 (79%) cases. Intra-observer agreement was 91% (Kappa = 0.82, 95% CI 0.89-0.93) with cytohistological correlation in 29 of 33 (87%) cases. Causes of diagnostic errors included marked dissociation, pleomorphism, poorly cellular smears from hyalinized fibrodenoma, lacational changes and apocrine metaplasia with cystic changes. Multinucleated giant cells were frequently encountered in FNA smears from fibroadenoma (31.8%), but in none of the lumpectomy specimens. Their histiocytic nature was suggested by immunohistochemistry. CONCLUSION: FNA was a highly sensitive method for the diagnosis of fibroadenoma. Current cytological criteria were reliable and gave high inter- and intra-observer reproducibility.