Breast cancer is the most common malignancy for women in manycountries.1Recent microarray studies of gene expression have demonstrated that breastcancer is a molecularly heterogeneous assemblage of different subtypescharacterized by distinct aberrations at the molecular level.2,3 Breast cancer can be classified into at leastfive distinct subtypes: luminal A, luminal B, human epidermal growth factorreceptor 2 (HER2) overexpressing, basal-like, and normal breast. This evidence concerns the gene ERBB2 and breast cancer.