Tubular Adenomas of the Breast Are Cytologically Distinct from Fibroadenomas

Introduction: Increasing molecular evidence indicates that tubular adenoma of the breast is distinct from fibroepithelial lesions, leading to its reclassification as an epithelial tumor in the 5th World Health Organization classification of tumors of the breast. However, tubular adenoma remains poorly characterized on fine-needle aspiration cytology (FNAC) and often not distinguished from fibroadenomas. In this study, the largest cohort, to date, of histologically confirmed aspirates of tubular adenomas were reviewed and compared with aspirates of fibroadenomas. Findings from this study further define the cytological features of tubular adenoma and allow differentiation from fibroadenoma. Methodology: Aspirates of histologically confirmed tubular adenomas were reviewed for features of the background, myoepithelial, epithelial, and stromal components and then compared to a cohort of aspirates of fibroadenomas. Results: Totally, 43 (tubular adenoma) and 94 (fibroadenoma) aspirates were included. Tubular adenomas displayed moderate epithelial cellularity with high cohesiveness, with stromal fragments containing epithelium. Tubules are more common in tubular adenomas (p = 0.009) and “tubular fragments” (tissue fragments containing multiple tubular structures with/without stroma) is a pathognomonic feature of tubular adenoma (p < 0.001). Calcification and fibrocystic changes were variably seen (4.65–13.5%) but without difference to fibroadenomas (p > 0.05). Cytomorphologically malignant features and mitoses were absent in all aspirates of tubular adenoma. Presence of tubules and stromal fragments were independent factors associated with tubular adenomas, whereas a predominance of large epithelial fragments and naked stromal fragments were associated with fibroadenomas. Conclusion: Tubular adenomas are not only histologically and molecularly separate from fibroepithelial lesions but also a distinct entity on FNAC.