In order to investigate whether the mevalonate pathway affects the sensitivity to MEK inhibitors, we treated human breast cancer MDA-MB-231 cells harboring KRAS and BRAF mutations with a MEK inhibitor, CH5126766, with or without statins, which inhibits HMG-CoA reductase, the rate-limiting enzyme in the mevalonate pathway. The gene discussed is HMGCR; the disease is breast carcinoma.