MAP2K4 and neoplasm: The JNK pathway has been reported to play a suppressive role in tumor development and metastasis, with studies revealing a MEK4 loss-of-function mutation in approximately 5% of human tumors (such as breast, biliary, and pancreatic cancers) from a variety of tissues, and the identification of a microchromosomal region containing the MEK4 gene revealed its ability to suppress cell metastasis [32,38,39,40].