Pathologic quiz case: a 93-year-old woman with an enlarged and tender left breast. Histiocytoid variant of lobular breast carcinoma.

Abstract

volving the entire breast, measuring 150 mm in maximum size, and extending to the medial and lateral margins, the dermis of the nipple skin, and within 1 mm of the deep margin. The tumor was composed of single files of large cells with focal targetoid growth around the normal breast structures (Figure, A). The neoplastic cells contained abundant foamy or finely granular pale pink cytoplasm (Figure, A, inset, and Figure, B), with occasional intracytoplasmic lumina identified (Figure, B, inset). The nuclei were uniform and round to oval; they had a fine chromatin pattern and a single prominent nucleolus. Mitotic figures were 4 per 10 high-power fields. Neoplastic cells were seen diffusely infiltrating through adipose tissue in scattered areas, mimicking the appearances of fat necrosis (Figure, C). Foci of lobular carcinoma in situ (LCIS) (Figure, A, arrows, and Figure, D, inset) admixed with the invasive tumor and in surrounding breast parenchyma were observed. No lymphovascular invasion was seen. Three of 12 lymph nodes examined contained metastatic carcinoma with morphologic findings similar to the primary tumor. Immunostaining for estrogen and progesterone receptors was negative. Immunostaining for HER-2 was strongly and diffusely (31) positive. Gross cystic disease fluid protein 15 (GCDFP-15) (Figure, C, inset) and androgen receptor were positive, whereas E-cadherin (Figure, D, and D inset), S100 protein, calretinin, a-inhibin, and CD68 were negative in neoplastic cells. What is your diagnosis?