Synchronous and bilateral oncocytic carcinoma of the breast: A case report and review of the literature.

Synchronous bilateral breast cancer is rare, and oncocytic carcinoma is an even rarer breast cancer histological subtype. In general, oncocytic tumors are defined as neoplasms with eosinophilic granular cytoplasm and have been reported in various organs. Oncocytic carcinoma of the breast was first documented by Gădăleanu and Craciun in 1987, and 48 cases have since been reported. The present study reports a case of synchronous bilateral breast oncocytic carcinoma. The patient was a 78-year-old woman. Although she exhibited no symptoms, chest computed tomography revealed three multinodular breast tumors: Two in the right breast and one in the left. Core needle biopsy was performed on the three tumors, and the patient was diagnosed with invasive ductal carcinoma with potential apocrine carcinoma. A bilateral modified radical mastectomy was performed. Surgical specimens of the three tumors revealed cord- or nest-forming tumor cells with eosinophilic granular cytoplasm. Immunohistochemically, the tumor cells were markedly positive for mitochondria. Electron microscopy of the tumor samples additionally revealed numerous mitochondria filling the cytoplasm. Based on these findings, the tumors were diagnosed as oncocytic carcinoma. The pathogenesis of oncocytic carcinoma remains to be fully elucidated; thus, additional clinicopathological studies are required.