Identification of BRAF mutations in eruptive melanocytic nevi: new insights into melanomagenesis?

Eruptive melanocytic nevi (EMN) is an unusual phenomenon characterized by the abrupt, simultaneous appearance of hundreds of melanocytic nevi on previously uninvolved sun-exposed skin. The mechanisms underlying this phenomenon are not well understood, but have been associated with both systemic immunosuppression and bullous dermatoses. The paper under evaluation brings new insight into the molecular events underlying EMN development in a patient receiving 6-mercaptopurine immunosuppressive therapy for ulcerative colitis. Sequencing of DNA from 20 eruptive nevi revealed the presence of BRAF V600E mutations in 85% of the lesions tested. The role of mutated BRAF in the initiation and progression of melanoma in conjunction with the strong correlation between nevus number and melanoma risk suggests the need for photoprotection in patients receiving thiopurine therapy. The study under evaluation further points to the possible interaction between environmental mutagens and UV radiation in the acquisition of BRAF mutations that may in turn increase the risk of melanoma development.