MAPK3 and cancer: SP enters the tumor, activates NK1R in cancer cells, and activates growth factor receptor through Src (EGFR, HER2) [3], and activates the MAPK pathway including extracellular signal-regulated kinases 1 and 2 (ERK1/2), to stimulate mitogenesis, induce cell proliferation, and avoid apoptosis by increasing the mRNA expression of MMP-2, MMP-9, VEGF, and VEGFR [131], which can also be produced by transactive EGFR and activation of NK-1R/Akt/NF-κB signaling pathway [132,133].