As a second messenger, low to moderate levels of ROS can regulate the activation or expression of multiple signalling proteins such as mitogen-activated protein kinase (MAPK), AMPK, protein kinase B (AKT), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) [24–29], all of which are involved in cancer cell survival, proliferation and stress response. Here, MAPK8 is linked to cancer.