MAPK3 and neoplasm: (a) Downregulates FOXO3a expression in tumor cells; (b) blocks the 5‐HT–5‐HT2BR–pERK–Yap axis; (c) blocks 5‐HT induced phosphorylation of ERK1/2 and eNOS; (d) inhibits 5‐HT‐mediated upregulation of STAB1 and SERPINB2 gene expression