Gynecomastia with unusual intraductal "clear cell" changes mimicking pagetoid ductal spread of lobular neoplasia.

This report describes a case of unusual intraductal "clear cell" changes of male breast that mimicked pagetoid ductal spread of lobular neoplasia. The lesion developed inside a nodule of gynecomastia of the left breast in a 56 year-old man. Immunohistochemically, the enlarged clear cells reacted positively with epithelial membrane antigen, low molecular weight cytokeratin and three breast markers (i.e.: gross cystic disease fluid protein-15 and -44 and estrogen receptors). They were negative for high molecular weight cytokeratin, muscle-specific actin, desmin and vimentin. Differential diagnoses included pagetoid ductal involvement by lobular neoplasia (i.e.: lobular carcinoma in situ and/or atypical lobular hyperplasia), pagetoid growth of intraductal carcinoma, atypical intraductal hyperplasia, and unusual intraductal myoepithelial proliferative lesion.