HER2 positive primary breast squamous cell carcinoma with good prognosis: a case report.

Background: Primary breast squamous cell carcinoma (PBSCC) is a unique histopathological type of breast cancer. The majority of current case reports of PBSCC are triple-negative tumors with poor prognosis. Due to its heterogeneous clinical course, no unified management is achieved. Here, we report a human epidermal growth factor receptor 2 (HER2) positive case with good clinical outcome, which may contribute to the development of appropriate guidelines and imprecise management of PBSCC.

Case description: A 45-year-old female presented with a painless mass in the medial-upper quadrants of right breast and the imaging examination suggested a malignant tumor. She received modified radical mastectomy and axillary sentinel lymph node dissection of the right breast, and the pathological diagnosis was squamous cell carcinoma with HER2 over-expression. Subsequently, she underwent post-operative chemotherapy regimen of doxorubicin, cyclophosphamide, T-docetaxel and trastuzumab (AC-TH) and then received maintenance treatment with trastuzumab and pertuzumab. Clinical follow-up suggests that she had achieved clinical complete remission and has survived for over 4 years.

Conclusions: The diagnosis of PBSCC relies on histomorphology, due to non-specific imaging manifestations. Immunohistochemical (IHC) staining helps to clarify the pathological type, hormone receptor status, HER2 amplification and programmed cell death ligand 1 (PD-L1) expression, which is essential for clinical decision-making. HER2-positive PBSCC patients can benefit from AC-TH chemotherapy and 1-year anti-HER2 therapy is necessary to good prognosis. If possible, dual anti-HER2 therapy combined with trastuzumab and pertuzumab is recommended. Finally, positive clinical prognosis of PBSCC may be attributed to early detection, immediate surgery, precise diagnosis and proper adjuvant treatment strategy.