Sorafenib is a potent inhibitor of several Raf kinase isoforms, including C-Raf, wild-type B-Raf and mutant B-Raf (e.g., V600E mutant b-raf), as evidenced by reduced phosphorylated (p)ERK levels and proapoptotic effects in human colon and pancreatic tumor cells (both K-ras), melanoma cells (b-raf V600E), and breast cancer cell lines (K-ras and b-raf G463V) at low nanomolar concentrations in vitro (1, 2). The gene discussed is KRAS; the disease is breast cancer.