2017 Volume 66 Issue 3 Pages 289-296
The invasive lobular carcinoma histiocytoid variant (histiocytoid breast carcinoma; HBC) is a rare variant that apparently shows apocrine differentiation. We report a case of HBC that exhibited a highly cellular smear pattern in fine-needle aspiration cytology (FNAC). The patient was a woman in her 80s. FNAC revealed numerous tumor cells in a mass in her left breast. The tumor cells were observed as loosely cohesive cellular clusters or scattered single cells. These cells with an abundant foamy cytoplasm and a low N/C ratio resembled histiocytes and occasionally showed an apocrine-like appearance with a rich granular cytoplasm. Histopathologically, she was diagnosed as having the invasive lobular carcinoma histiocytoid variant (HBC). Immunohistochemically, the tumor cells were positive for p120, GCDFP-15, CD68, and androgen receptor, and negative for E-cadherin, adipophilin, ER, PgR, and HER2. The Ki-67 positivity rate was 2%, and p53 stained weakly (5–10%). Alcian blue diffusely stained the tumor cells. The diastase-resistant PAS reaction was positive in the prominent eosinophilic granular cytoplasm but was negative or partially positive in the slightly eosinophilic foamy cytoplasm, which was more strongly positive for GCDFP-15. HBC showed a close resemblance to pleomorphic invasive lobular carcinoma (PILC) in its smear pattern and mucin-positive cytoplasm, but the nuclear atypia, Ki-67 positivity rate, and HER2 and p53 expression levels were considered useful for distinguishing HBC from PILC. The apocrine features of HBC were incomplete in the sense that adipophilin was negative.
