Breast Adenomyoepithelioma Mimicking Fibroadenoma on Cytology: A Diagnostic Pitfall

Background: Adenomyoepithelioma (AME) of the breast is a rare biphasic neoplasm composed of epithelial and myoepithelial cells. Its diverse morphology frequently leads to diagnostic challenges, particularly on cytology where it may mimic benign fibroepithelial lesions. Case Presentation: We report a case of breast adenomyoepithelioma in a 25-year-old woman presenting with a well-circumscribed, painless breast lump. Radiological evaluation suggested a benign lesion (BI-RADS 2/3). Fine needle aspiration cytology favored a benign fibroepithelial lesion, likely fibroadenoma. However, histopathological examination of the excision biopsy specimen revealed a well-circumscribed biphasic tumor composed of ductal epithelial and proliferating myoepithelial cells. Immunohistochemistry demonstrated myoepithelial differentiation with positivity for smooth muscle actin (SMA) and p63, confirming the diagnosis of adenomyoepithelioma. The excision margins were negative. The patient has been followed up for 24 months to date, with no evidence of recurrence.Conclusion: This case highlights the limitations of cytology in diagnosing rare biphasic breast tumors and underscores the importance of histopathological evaluation with immunohistochemistry for accurate diagnosis. Awareness of this entity is essential to avoid misdiagnosis and ensure appropriate management.