A Case Report of Lipid-Rich Carcinoma of the Breast Including Histological Characteristics and Intrinsic Subtype Profile

A 57-year-old Japanese woman with schizophrenia, who had received long-term treatment with neuroleptics, noticed a painless, pea-sized lump in her right breast. She was admitted to our hospital and a malignant tumor was diagnosed. The patient underwent a conservative radical mastectomy (Patey's operation). The excised tumor measured 2.0 x 1.2 x 1.1 cm in diameter, and its cut surface was grayish-white. Histologically, tumor cells with clear to foamy cytoplasm were invariably Oil Red O-positive and periodic acid Schiff-negative with or without diastase digestion. The tumor was diagnosed as a lipid-rich carcinoma accompanied by an in situ component. Neuroleptics increase serum prolactin levels by interfering with dopaminergic inhibition of prolactin secretion. Immunohistochemical analysis revealed that, although prolactin was not detected, the tumor cells expressed prolactin receptor, indicating prolactin as the genesis of this neoplasm. In immunohistochemical intrinsic subtype analysis, the tumor was negative for estrogen receptor, progesterone receptor, human epidermal growth factor receptor 1 and 2, and basal cytokeratins (CK5, CK6, and CK14), indicating an unclassified (all-marker negative) subtype. Axillary lymph nodes were free of metastasis (stage I), and the patient has been well for 20 years without any evidence of recurrence.