Strikingly, there was poor treatment efficacy among heterogenous tumors, with pCR of 55% in non-heterogeneous tumors versus 0% in heterogenous tumors, 75% of which were IHC2+/ISH+.35 With rising interest in antibody drug conjugate therapy, tumor heterogeneity may become a relevant marker for selecting HER2+ patients who stand to gain greatest therapeutic benefit, but further studies are needed to integrate this parameter into practice. This evidence concerns the gene ERBB2 and neoplasm.