Histiocytoid breast carcinoma: a case report showing immunohistochemical profiles.

Histiocytoid breast carcinoma (HBC) is a rare type of breast cancer with a controversial histogenesis. Here we describe a case report of a 65-year old woman with HBC. The patient presented with two masses in the right breast. Histopathologically, the tumors consisted of a diffuse infiltration of large tumor cells and histological components of carcinoma in situ and atypical lobular hyperplasia were also observed. The infiltration pattern was similar to that of invasive lobular carcinoma with targetoid and Indian file arrangements. The invasive histiocytoid cells had finely granular, eosinophilic to vesicular cytoplasm and nuclei with a bland uniform appearance, a single small eosinophilic nucleolus and finely granular chromatin. We compared the immunohistochemical profiles of 17 breast cancer markers between invasive carcinoma, carcinoma in situ, atypical lobular hyperplasia and normal breast epithelium. Although they all shared the same reactivity for many of the proteins, they exhibited differences in GCDFP-15, E-cadherin, P120, CEA, HER-2, ER and PR expression, and these are discussed. This is the first case study of two HBC masses occurring in one breast simultaneously. By analyzing and comparing their morphologic characteristics and spectrum of immunohistochemical expression, our study supports the view that HBC is a variant of lobular carcinoma and our findings may assist in future diagnoses of HBC.