OPN4 and non-small cell lung carcinoma: Considerable evidence has shown that GPCR activation can promote the phosphorylation of its huge downstream corresponding factors, such as PI3k/Akt/mTOR (78) and PCK/RAF/MEK/ERK (79), thereby promoting the development of NSCLC—for example, Opsin 4/opiomelanocortin (OPN4) (79), a member of the Opsin family of GPCRs, is overexpressed in NSCLC patients and correlated with survival.