Apocrine ductal carcinoma in situ involving a sclerosing lesion with adenosis: report of a case.

Apocrine metaplasia is a ubiquitous component of the mammary fibrocystic change spectrum. Although mostly associated with cysts, apocrine metaplasia can also present as a proliferative lesion, rarely with cytologic atypism. Apocrine atypia is characterized by 3-fold nuclear enlargement, multiple nucleoli, and hyperchromatism and generally arises in florid adenosis or radial sclerosing lesions. Dramatic apocrine atypia may be very difficult to distinguish from apocrine ductal carcinoma in situ. The latter is distinguished from apocrine atypia by greater extent of the lesion (>0.4 cm) and the presence of greater nuclear pleomorphism with nuclear membrane irregularity. The clinical significance of apocrine atypia is poorly understood and reflects the lack of published outcome studies. Herein, I report a case in which apocrine ductal carcinoma in situ presented as "atypical apocrine adenosis" in a needle core breast biopsy. It illustrates the problem of assessing apocrine atypia and apocrine ductal carcinoma in situ in small samples.