Accumulating evidence has also demonstrated that β-adrenergic receptors mediate the proliferative and anti-apoptotic effects of NNK in non-lung cancer cells.[32] Furthermore, the mitogenic effects of NNK have been found to be mediated by β-adrenergic receptors, indicating that NNK promotes the growth of gastric cancers via PKC and ERK1/2 phosphorylation in a β-adrenergic receptor-dependent fashion.[33, 34] Our previous results showed that NNK induces HNSCC cell proliferation through a α7-nAChR–EGFR signaling axis to facilitate the growth of HNSCC. This evidence concerns the gene MAPK3 and head and neck squamous cell carcinoma.