MAPK1 and neoplasm: In 2016, when Brenan and co-workers used saturation mutagenesis to comprehensively characterize the activity and drug sensitivity of a wide range of ERK2 mutants, they identified a rare ERK2 mutant that is found in human tumours and is associated with gain- or loss-of-function activity (GOF, LOF) and a differential responsiveness to MAPK-directed therapies [52].