MAPK3 and neoplasm: Whereas, for the ERK1/2 pathway, specific somatic mutations in BRAF or NRAS (such as BRAFV600E or NRASQ61K/L) cause ERK1/2 pathway activation and drive tumour cell proliferation, survival and motility, somatic mutations in ERK5 signalling pathway components are rare and none have been detected with high frequency.