MAPK9 and cancer: JNK/SAPK (isoforms JNK-1, JNK-2 and JNK-3), p38 MAPK (isoforms p38α, p38β, p38γ and p38δ) and ERK1/2 pathways belong to the MAPK family and are involved in different cellular responses, including both cancer cell proliferation and cell death.