CHRNA7 and small cell lung carcinoma: Studies have shown that nicotine or NNK stimulates the release of autocrine growth factors serotonin and mammalian bombesin in a dose-dependent manner by binding to α7nAChRs (Cattaneo et al., 1993), which subsequently activates downstream protein kinase C (PKC)/Raf-1/mitogen-activated protein kinase (MAPK)/c-Myc mitogenic signaling pathway and promotes the growth of SCLC cell subpopulations in vitro (Jull et al., 2001).