By revealing the role of HIF-1α in regulating the hypoxia response and showing that this mechanism, as well as the expression of additional features, link HER2 related tumors in subgroup 7 with basal-like breast tumors and subgroup 10 tumors with luminal like breast tumors, respectively, we identify additional oncogenic mechanisms and HER2 related tumor heterogeneity that was not previously evident. This evidence concerns the gene HIF1A and breast neoplasm.