Melanoma genome sequencing reveals frequent PREX2 mutations

Whole-genome sequencing of 25 metastatic melanomas and matched germline DNA in humans reveals that the highest mutation load is associated with chronic sun exposure, and that the PREX2 gene is mutated in approximately 14 per cent of cases Melanoma is a highly metastatic cancer, characterized by high lethality and rapid development of resistance to treatment. Whole-genome sequencing of 25 metastatic melanomas and matched germline DNA reveals that the mutation rate varies widely, with the highest mutation load associated with chronic exposure to sunlight. PREX2 — a PTEN-interacting protein previously implicated in breast cancer — is mutated in approximately 14% of cases. Although the precise role of PREX2 in melanoma remains to be elucidated, ectopic expression of its mutant form accelerates tumour formation of immortalized human melanocytes in vivo. Melanoma is notable for its metastatic propensity, lethality in the advanced setting and association with ultraviolet exposure early in life1. To obtain a comprehensive genomic view of melanoma in humans, we sequenced the genomes of 25 metastatic melanomas and matched germline DNA. A wide range of point mutation rates was observed: lowest in melanomas whose primaries arose on non-ultraviolet-exposed hairless skin of the extremities (3 and 14 per megabase (Mb) of genome), intermediate in those originating from hair-bearing skin of the trunk (5–55 per Mb), and highest in a patient with a documented history of chronic sun exposure (111 per Mb). Analysis of whole-genome sequence data identified PREX2 (phosphatidylinositol-3,4,5-trisphosphate-dependent Rac exchange factor 2)—a PTEN-interacting protein and negative regulator of PTEN in breast cancer2—as a significantly mutated gene with a mutation frequency of approximately 14% in an independent extension cohort of 107 human melanomas. PREX2 mutations are biologically relevant, as ectopic expression of mutant PREX2 accelerated tumour formation of immortalized human melanocytes in vivo. Thus, whole-genome sequencing of human melanoma tumours revealed genomic evidence of ultraviolet pathogenesis and discovered a new recurrently mutated gene in melanoma.