BRAF and melanoma: Given that MAPK pathway activation is the key downstream effector of BRAFV600E, and that effective targeting of this pathway is a current standard-of-care for BRAF-mutant melanoma, we tested the efficacy of the MEK1/2 inhibitor, selumetinib (AZD6244; ref. 43), in PREX2-deficient versus -proficient BRAF PTEN and BRAF P53 melanoma.