Breast carcinoma in a fibroadenoma: diagnosis by fine needle aspiration cytology.

We describe a case of ductal carcinoma in situ (DCIS) occurring in a fibroadenoma diagnosed by fine needle aspiration (FNA) cytology. The cytological features comprised a small population of pleomorphic cells admixed with a dominant population of bland epithelial cells showing features consistent with those of a fibroadenoma. Excision biopsy confirmed the presence of DCIS within an otherwise typical fibroadenoma. Recent reviews have emphasised the potential for fibroadenoma to cytologically mimic carcinoma, leading to false positive findings, however the converse is also possible. We conclude that a false negative cytological diagnosis may be avoided by recommending histological confirmation by excision biopsy when significant atypia is present, even if the overall pattern is that of a fibroadenoma.