Concurrent Eruptive Melanocytic Nevi and Multiple Keratoacanthomas Induced by Encorafenib

Eruptive melanocytic nevi and multiple keratoacanthomas are rare cutaneous conditions, often linked to drug-related toxicities but rarely reported simultaneously, particularly in cancer patients undergoing BRAF-targeted therapies. We present a case of a 64-year-old male with metastatic colorectal cancer who developed severe pruritus and widespread new skin lesions following treatment with encorafenib, a v-Raf murine sarcoma viral oncogene homolog B (BRAF) inhibitor, and panitumumab, an anti-epidermal growth factor receptor (EGFR) monoclonal antibody. The dermatological assessment identified both pigmented and non-pigmented lesions, including benign nevi and keratoacanthomas. Despite close monitoring, larger keratoacanthomas persisted, prompting surgical excision, which confirmed lichenoid keratosis. The Naranjo scale indicated a definite association between encorafenib and cutaneous reactions, with a score of nine. The mitogen-activated protein kinase pathway's role in cutaneous adverse events was explored, suggesting a paradoxical activation mechanism. Discontinuation of encorafenib and panitumumab led to gradual resolution of most lesions, highlighting a possible etiopathogenic link. This study emphasizes the need for thorough dermatologic evaluation and follow-up in patients receiving BRAF inhibitors to optimize management and avoid unnecessary treatment cessation.