Previously, we reported that MAP3K4 associates with tyrosine phosphorylated HER3 in response to HRG stimulation of MCF-7 and T-47D breast cancer cells and, we showed that HER2 activity was required for the association between MAP3K4 and HER3, but HER2 was not present in this complex of proteins24. This evidence concerns the gene ERBB3 and breast cancer.