To elucidate the molecular mechanisms underlying the down‐regulation of SIRT1 by metformin in NSCLC cells with different LKB1 statuses, we studied effects of metformin on down‐regulation of SIRT1 in NSCLC cell lines (A549, H1299, H460 and H226). The gene discussed is SIRT1; the disease is non-small cell lung carcinoma.