MAPK3 and cancer: Due to the well-established role of ROS in cell signaling, cancer cells always have higher levels of endogenous ROS to enhance rapid cell growth and proliferation through the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinase 1/2 (ERK1/2), phosphoinositide-3-kinase (PI3K)/Akt, nuclear factor-κB (NF-κB), and hypoxia-sensitive α (HIF1α) pathways [13,14,15,16,17,18].