FINAL DIAGNOSIS: INFILTRATING DUCTAL CARCINOMA WITH APOCRINE FEATURES
Apocrine change or differentiation is characterized by cells that are larger than usual and have abundant, granular eosinophilic cytoplasm, distinct cell borders, and luminal apical blebbing. Nuclei are eccentrically located, variable in size and either vesicular or hyperchromatic, usually with prominent nucleoli. A second type of apocrine cell has a pale, foamy cytoplasm caused by numerous vesicles. The nuclei are similar to those of the first type (1). Cell of apocrine carcinoma show strong cytoplasmic staining with antibody to gross cystic disease fluid protein-15, cytokeratin AE1, CEA, androgen receptor and c-erbB-2 oncoprotein. Vimentin and S100 are negative (2).
Varying degrees of apocrine differentiation can be seen in most types of benign breast lesions (e.g. fibrocystic change, fibroadenoma, and adenosis) and many malignancies including invasive ductal carcinoma, invasive lobular carcinoma, and both ductal and lobular carcinoma in situ (3). Tumors entirely or predominately composed of apocrine cells ("apocrine carcinomas") account for less than 0.5% of all breast carcinomas (4). In one series of 2000 cases of primary breast carcinoma, 6 (0.3%) met morphologic and immunohistochemical criteria for apocrine carcinoma (2). Some studies have estimated the incidence to be anywhere from 15% to 60%, however this likely reflects lack of objective criteria and possible confusion with other eosinophilic and granular cell tumors of the breast.
Many researchers do not recognize apocrine carcinoma as a distinct clinicopathologic entity as most studies have found no significant differences in natural history and prognosis relative to regular infiltrating ductal carcinoma. However, because of substantial differences in hormone expression between apocrine lesions and similar common epithelial derived lesions, future treatment modalities may be quite different. For the time being, therapy for apocrine carcinoma is identical to that for infiltrating ductal carcinoma (6).
Contributed by Kate McFadden, MD and Malathy Kapali, MD