Background: Breast cancers arising in women with germline BRCA1 mutations are most likely to be estrogen receptor (ER), progesterone receptor (PR), and HER2/neu negative (so-called triple negative or basal-like breast cancers). Metaplastic carcinoma with pure squamous differentiation is a very rare histological subtype (0.1% of all breast cancers) and is usually ER, PR, and HER2/neu negative by immunohistochemistry. A BRCA1 germline mutation in squamous cell breast cancer has never been reported.
Case report: A 25-year-old woman was diagnosed with squamous cell cancer of the breast. Three years later, she developed contralateral breast cancer, also of the squamous cell subtype. Both tumors were triple negative. Because of the patient's history and her strong family history, genetic testing was recommended. The patient was found to be carrier of a BRCA1 germline mutation.
Conclusion: We report, to our knowledge, the first case of a BRCA1 mutation in a woman with metaplastic squamous cell breast cancer.