Histiocytoid breast carcinoma, neither lobular nor ductal? A case report and literature review.

Histiocytoid breast carcinoma (HBC) is a rare type of breast cancer with controversial histogenesis, which is characterized by abundant foamy cytoplasm, fuzzy cell boundary, linear or annular infiltration, eccentric large irregular nuclei or prominent nucleoli and low mitotic activity. HBC has been considered to be a variant of lobular carcinoma, a variant of apocrine ductal carcinoma, and an apocrine variant of lobular carcinoma and to resemble lipid-rich carcinoma. We presented a case of 75-year-old woman with a 5-cm mass in the left breast. The mass was yellow-beige on cut section. HBC was diagnosed including invasive carcinoma (IC) of apocrine differentiation (diameter about 5 mm) which was surrounded by extensive carcinoma in situ (CIS, diameter about 25 mm) of apocrine type, and a 4-mm invasive ductal carcinoma (IDC) in grade II. The distance between HBC and IDC was 4 mm. There was extensive (42 of 43 lymph nodes) metastasis and intravascular tumor emboli. The tumor extended into peripheral nerve. The pathology showed histiocytoid breast carcinoma with a smaller conventional invasive ductal carcinoma in adjacent area. She received a left modified radical mastectomy. However, on the follow-up imaging techniques, the mass showed no response. We discussed the pathology and immunohistochemical finding, and reviewed the literatures. We found that this case was a unique type of HBC.