A rare case of HER2-positive pure metaplastic squamous cell carcinoma of the breast.

Primary squamous cell carcinoma of the breast (PSCCB) is a rare form of metaplastic breast carcinoma (MpBC), constituting approximately 0.1% of all invasive breast cancers. It is characterized by unique morphological and clinical features, exhibiting a high degree of invasiveness and a poor prognosis. Most molecular subtypes are negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), while HER2-positive PSCCB is even rarer, accounting for approximately 4-22% of cases. Accurate histological diagnosis is crucial for effective management.Currently, there is limited research on neoadjuvant chemotherapy combined with targeted therapy for HER2-positive PSCCB, and standardized treatment protocols have yet to be established. We report a case of pure HER2-positive PSCCB with the aim of gaining experience in the treatment of HER2-positive PSCCB.