Eruptive Melanocytic Nevi in the Setting of Encorafenib, Cetuximab, and Binimetinib Combination Therapy: A Case Report.

Introduction: The development of new and changing melanocytic lesions has been increasingly reported as an adverse dermatologic toxicity of BRAF inhibitor therapy. Melanocytic lesions and melanomas induced by BRAF inhibitor therapy that lack BRAF V600E expression have been less commonly described. One mechanism that has been proposed for the development of BRAF inhibitor-induced melanocytic lesions, including those lacking BRAF V600E expression, is the paradoxical activation of the MAPK signaling pathway in BRAF wild-type (BRAF^WT) cells.

Case presentation: Herein, we report a rare case of a 39-year-old woman who developed numerous BRAF V600E-negative eruptive melanocytic nevi following encorafenib, cetuximab, and binimetinib combination therapy, the current standard of care for the treatment of BRAF-mutant metastatic colorectal cancer.

Conclusion: Patients treated with BRAF inhibitors, with or without related combination therapies, who develop BRAF^WT melanocytic lesions are at risk for developing both dysplastic nevi and melanoma, thereby warranting baseline dermatoscopic evaluation prior to the initiation of therapy as well as regular follow-up during and after treatment.