To identify the determinants of sensitivity to TAK-285, we examined the relationship between the IC50 values of TAK-285 for cell growth inhibition and EGFR, HER2, HER3, HER4, phosphatase and tensin homolog (PTEN), and IGF-1R gene expression in a panel of human breast cancer cell lines, other types of cancer cells, and non-transformed cells in vitro. The gene discussed is ERBB3; the disease is breast cancer.