HRG and cancer: To investigate growth factor-induced proliferation we screened a panel of 58 cancer cell lines (10 ovarian cancer, 11 breast cancer, 13 lung cancer, 11 gastric cancer, and 23 colorectal cancer cell lines) for response to the exogenously added ligands EGF, HRG, HGF, and IGF-1 (Supplementary Fig. 1) that bind to EGFR, ErbB3, Met, and IGF-1R, respectively.