Primary Squamous Cell Carcinoma of the Breast: A Case Report and Comprehensive Literature Review

Primary squamous cell carcinoma (SCC) of the breast is one of the rarest forms of metaplastic breast carcinoma. It is typically triple-negative, high-grade, and is associated with aggressive clinical behavior. As it is an extremely rare condition, there is no standardized treatment protocol. We present a case of primary SCC of the breast in a postmenopausal woman who presented with a rapidly growing mass of the breast and an inverted nipple. Histopathology confirmed the diagnosis of SCC of the breast, and immunohistochemistry revealed diffuse p40 positivity. The patient underwent bilateral mastectomy and axillary lymph node dissection, followed by adjuvant chemotherapy and immunotherapy. The patient completed chemotherapy, but immunotherapy had to be stopped due to immune-related endocrine toxicity. This case highlights the diagnostic challenges, treatment modalities, and the emerging role of immunotherapy in this rare subtype of breast cancer.