We then subjected RT2 tumor-derived cancer cell lines (BTC3 and BTC4) to treatment with the gefitinib EGFR inhibitor, after profiling of Egf family ligands and Erbb receptors in these BTC cell lines revealed that they express the same family members in vitro (Egfr, Tgf-α, and Hb-egf) as the cognate tumors do in vivo (Supplementary Figs. S4 B and C). Here, EGFR is linked to cancer.