A Case Report of a Rare ER+, PR- Pure Metaplastic Breast Squamous Cell Carcinoma with HER2 Overexpression.

BACKGROUND Breast squamous cell carcinoma (SCC) is a subtype of metaplastic breast carcinoma (MBC), which is a rare malignancy and accounts for 0.1% of all invasive breast carcinomas. Guidelines on definitive management and treatment of breast SCC are not well established, given its rarity and diverse immunohistochemistry (IHC) profile, and lack of clinical data.