Mixed pleomorphic lobular and apocrine carcinoma of the breast: A case report suggesting pathogenesis.

Pleomorphic lobular carcinoma (PLC) of the breast is a variant of lobular carcinoma, characterized by loss of E-cadherin expression and high-grade morphologies. Whether the pathogenesis of PLC is in the ductal or the lobular lineage has been discussed. In this report, a case of PLC combined with apocrine carcinoma is presented. Histologically, the tumor showed two distinct carcinoma components: one was a typical apocrine carcinoma, and the other was a pleomorphic invasive lobular carcinoma. The former showed complete membranous expression of E-cadherin, whereas the latter aberrantly expressed it not on the cell membrane, but in the cytoplasm. Both components were triple-negative and strongly positive for GCDFP-15, suggesting apocrine differentiation. The intraductal component showed only a feature of apocrine ductal carcinoma in situ. This case suggests that apocrine carcinoma could be an origin of PLC.