BACKGROUND: Breast metaplastic squamous cell carcinoma (SCC) is a rare primary breast carcinoma, and overexpression of HER2 in this carcinoma is extremely uncommon.

CASE REPORT: We presented a case of a 48-year-old Asian female with breast metaplastic SCC. Fine needle aspiration biopsy (FNAB) and core needle biopsy (CNB) of the lesion were taken prior to surgical resection. FNAB smears demonstrated highly atypical squamous cells and a diagnosis positive for malignancy was rendered. CNB and a surgical resection specimen revealed invasive squamous carcinoma with keratin pearl formation and intercellular bridges. Further study demonstrated this was an unusual metaplastic SCC case with basal-HER2 (+) phenotype. HER2 has been linked to poor prognosis and response to therapy.

CONCLUSIONS: The pathological diagnosis of the breast metaplastic SCC was made initially by FNAB and CNB. Identification of basal-HER2 (+) phenotype was critical for selection of hormonal therapies and chemotherapy.

Keywords: Genes, erbB-2, Mass Behavior, Metaplasia, Neoplasms, Squamous Cell