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Primary squamous cell carcinoma of the breast with unusual basal-HER2 phenotype.

OBJECTIVES
To report three cases of primary squamous cell carcinoma of the breast with an unusual "basal-HER2" phenotype.


METHODS
Clinical data were analyzed. Morphological features were observed. Immunohistochemical study for ER, PR, HER2, Ki-67, CK 5/6, CK10/13, CK14, EGFR, P63 and FISH detection of HER2 gene amplification were performed.


RESULTS
Three patients were all female with 26, 57 and 66 years old. The tumors were 3 cm, 4 cm and 5 cm in size respectively. Morphologically, all three tumors were pure squamous cell carcinoma and entirely composed metaplastic squamous cells. Two tumors were moderately differentiated and one was poorly differentiated. All three patients were positive for P63 or CK10/13. All three tumors exhibited basal-HER2 phenotype: negative for ER and PR, positive for HER2 protein and HER2 gene amplification, and positive for at least two basal markers.


CONCLUSIONS
SCC with basal-HER2 phenotype is an extremely rare subset of breast carcinoma. Since it may have worse prognosis than typical basal-like SCC, recognization of this unusual SCC in routine work may have obvious clinical significance.