Indeed, Bendell and colleagues also demonstrated a PR in cholangiocarcinoma treated with a MEK 1/2 inhibitor.[17] Although KRAS mutations may sensitize a tumor to MEK inhibitors,[18] the KRAS status of our patient with prolonged stable disease on a novel MEK inhibitor was unknown due to lack of tissue available for molecular analysis. The gene discussed is MAP2K1; the disease is cholangiocarcinoma.