EGFR and breast cancer: For example, gefitinib initially inhibited the growth of the EGFR-positive DU145 prostate cancer cell line and of MCF-7-derived tamoxifen- and fulvestrant-resistant breast cancer cell lines, but chronic exposure to gefitinib resulted in the development of gefitinib-resistant variant sublines, all of which showed upregulation of multiple IGF-1R signaling components when compared with their parental cell lines [54].