MCF7 cells are susceptible to the estrogen-ER signaling pathway-targeting agents like tamoxifen but resistant (relatively insensitive) to the EGFR/ERBB2 signaling-pathway inhibitors, including Afatinib and CP724714 (Genomics of Drug Sensitivity in Cancer, https://www.cancerrxgene.org/) (Fig. 4I, left panel). Here, ESR1 is linked to cancer.