Histiocytoid breast carcinoma: an apocrine variant of lobular carcinoma.

Two cases of in situ and invasive histiocytoid breast carcinoma are described. The invasive components of both tumours showed architectural and cytological similarities to lobular carcinoma. The in situ components showed areas of classical lobular carcinoma in situ, areas of lobular carcinoma with apocrine features and areas with transitional features. It is concluded that histiocytoid carcinoma represents an apocrine variant of lobular carcinoma. Differentiation of this tumour from chronic sclerosing inflammation may be difficult in both primary and secondary lesions.