Cobimetinib, which inhibits an enzyme known as MEK, has received approval to treat melanoma that has metastasized or can’t be surgically removed. The drug, marketed as Cotellic, is to be used in combination with vemurafenib (http://1.usa.gov/1RLrgf4).
Together, both drugs target melanoma tumors with BRAF V600E or V600K mutations. Found in about half of melanomas, mutated BRAF causes abnormal signaling in cancer cells, leading to tumor growth (http://bit.ly/1ML7H26). While vemurafenib inhibits some mutated forms of BRAF, cobimetinib blocks some forms of MEK, which is part of the same cell signaling pathway.
Rebecca Voelker. Two Melanoma Drugs Better Than 1. JAMA. 2015;314(23):2497. doi:10.1001/jama.2015.16798