MEK stands for MAPK/ERK kinase because of its role in activating the MAPK/ERK pathway; other names for this kinase are MAP2K and MAPKK. Because of its activity upstream of this pathway, MEK affects cellular processes such as proliferation, differentiation, and transcription. There are seven genes that make up MEK (named MAP2K1, MAP2K2, MAP2K3, and so on) and inhibitors to MEK can act on one or more of these targets. For example, the MEK inhibitor trametinib inhibits MAP2K1 and MAP2K2 only. Trametinib was FDA approved for treatment of metastatic melanoma in 2013. Other MEK inhibitors are currently undergoing preclinical and clinical trials for various cancers in which MAPK/ERK is overactive especially BRAF-mutated melanomas and KRAS/BRAF mutated colorectal cancer.