To evaluate the clinical significance of gene expression-based classification and define the characteristic features of the new basal-like subtype, invasive breast carcinomas were divided into ER, HER2, basal-like and null subtypes by immunohistochemical analysis. A total of 401 invasive breast carcinomas were submitted to tissue microarray and stained with ER, HER2, EGFR, c-KIT and cytokeratin (CK) 5/6. The basal-like tumors, defined as positive for one or more basal markers but negative for both ER and HER2, comprised 18.5%. They were larger (p=0.041), showed higher grade (p<0.001), and more frequently expressed p53 (p=0.003). Expression of the basal marker itself showed negative prognostic effect, particularly in node-positive group. Even ER-positive patients had far shorter disease-free survival (DFS) when the tumor coexpressed one or more basal marker (p<0.001). Discrimination of basal-like subtype or tumors positive for basal markers may be clinically significant also in the treatment and prognosis of breast carcinomas.

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