IGF1 and lung carcinoma: Furthermore, metformin inhibited nicotine‐derived nitrosamine ketone (NNK)‐induced lung cancer cell proliferation in mice by decreasing the levels of circulating insulin and insulin‐like growth factor 1 (IGF‐1), which suppressed the insulin/IGF‐1 signaling (IIS) pathway and the downstream mTOR signaling pathway.40