An orally bioavailable small-molecule inhibitor of mitogen-activated protein kinase kinase 1 (MAP2K1 or MEK1), with potential antineoplastic activity. Cobimetinib specifically binds to and inhibits the catalytic activity of MEK1, resulting in inhibition of extracellular signal-related kinase 2 (ERK2) phosphorylation and activation and decreased tumor cell proliferation. Preclinical studies have demonstrated that this agent is effective in inhibiting the growth of tumor cells bearing a B-RAF mutation, which has been found to be associated with many tumor types. A threonine-tyrosine kinase and a key component of the RAS/RAF/MEK/ERK signaling pathway that is frequently activated in human tumors, MEK1 is required for the transmission of growth-promoting signals from numerous receptor tyrosine kinases. or A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Cobalamin helps make red blood cells, DNA, RNA, energy, and tissues, and keeps nerve cells healthy. It is found in liver, meat, eggs, poultry, shellfish, milk, and milk products. Cobalamin is water-soluble (can dissolve in water) and must be taken in every day. Not enough cobalamin can cause certain types of anemia (a condition in which the number of red blood cells is below normal) and neurologic disorders. It is being studied with folate in the prevention and treatment of some types of cancer. Also called cyanocobalamin and vitamin B12.