More recently, the EGFR-selective tyrosine kinase inhibitor gefitinib has been shown to inhibit the growth of EGFR-positive MCF-7-derived tamoxifen-resistant breast cancer cells, an effect that can be abrogated by exposing the cells to non-EGF ligands such as heregulin-β and IGF-II [52]. This evidence concerns the gene EGFR and breast cancer.