Apocrine carcinoma with marked sebocyte-like cytological features: A report of two cases.

Apocrine carcinoma cases with sebaceous differentiation have not been reported and can be misdiagnosed as sebaceous carcinoma. We present two cases of apocrine carcinoma with marked sebocyte-like cytological features. Tumors were observed in the left axilla of a 68-year-old man (Case 1) and the right axilla of a 72-year-old man (Case 2). Both patients presented with multiple lymph node metastases. Histopathology revealed densely distributed solid nests of tumor cells containing foamy cytoplasm and enlarged round nuclei with prominent nucleoli. The tumor cells diffusely expressed adipophilin, PRAME (cytoplasmic pattern), androgen receptor, BerEP4, and GCDFP15 but did not express p63 in both cases. PIK3CA E726K and H1047R mutations were detected in Cases 1 and 2, respectively. Tumor location in the axilla, the presence of eosinophilic granular cytoplasm, prominent nucleoli, and PIK3CA mutations, immunoreactivity for BerEP4 and GCDFP15, and lack of p63 immunoexpression findings matched apocrine carcinoma characteristics, but not sebaceous carcinoma. Thus, apocrine carcinoma can demonstrate intracytoplasmic lipid accumulation and rarely exhibit sebocyte-like cytological features. Apocrine carcinoma should be distinguished from sebaceous carcinoma due to the former's higher metastatic potential and lack of association with Muir-Torre syndrome.