Moulder et al. utilized gene expression profiling on dasatinib-sensitive and -resistant cell lines to develop three potential predictive signatures of dasatinib sensitivity or resistance: a dasatinib sensitivity index, a Src pathway activity index, and a dasatinib target index.27 Among 133 breast cancer samples, the signatures identified distinct subsets that were predicted to be sensitive to dasatinib. The gene discussed is SRC; the disease is breast cancer.