Basal-HER2 Phenotype Shows Poorer Survival Than Basal-like Phenotype in Hormone Receptor-negative Invasive Breast Cancers

Previous studies have shown conflicting results on prognostic significance of basal-like breast tumors, but hormone receptor is a confusing factor in most of the prognostic evaluations. We aimed to characterize the prognostic features of basal-like tumors without the influence of hormone receptor status in a series of hormone receptor-negative breast tumors. Using tissue microarray and immunohistochemistry methods, according to the expression of HER2 and basal markers (CK5/6, CK14, EGFR), we categorized 713 consecutive hormone receptor-negative invasive breast cancers into 3 subtypes: HER2 (HER2+), basal-like (HER2-, any basal marker+), and null (HER2-, all basal markers-). The HER2 phenotype was subdivided into pure-HER2 (HER2+, all basal markers-) and basal-HER2 (HER2+, any basal marker+) subgroups. Expression of p53, p63, vimentin, and BRCA1 was assessed immunochemically. Basal-like tumors showed significantly higher grade, more frequent recurrence, and higher expression of vimentin and p63 than HER2 and null phenotypes. Basal-HER2 phenotype had significantly younger mean age and expressed a higher level of p53 and vimentin like basal-like and/or HER2 phenotypes. However, unlike all the other hormone receptor-negative phenotypes, they highly expressed BRCA1. No significant difference was found in 5-year survival among basal-like and the other hormone receptor-negative phenotypes, except for basal-HER2, which showed poorer 5-year overall survival than basal-like tumors. In conclusion, although basal-like breast tumors have distinct clinicopathologic and immunohistochemical features, they have similar 5-year survival compared with the other hormone receptor-negative tumors including HER2 and null phenotypes. However, there exists a small group of hormone receptor-negative tumors expressing HER2 and basal markers simultaneously. This small group of tumors showed significantly poorer 5-year overall survival than basal-like breast tumors and might require different treatment strategy.