Squamoproliferative lesions arising in the setting of BRAF inhibition.

In recent years, there has been increasing use of several novel agents that specifically target the V600E BRAF mutation in melanoma and other malignancies. One significant side effect of these drugs is the development of cutaneous squamoproliferative lesions, variously described as keratoacanthomas (KAs) and well-differentiated squamous cell carcinomas. We undertook a histopathological review of lesions excised from patients on BRAF inhibitor therapy, and found that 73% of lesions were squamoproliferative in nature. Of these, 33% met histologic criteria for a diagnosis of keratoacanthoma, whereas 43% showed features more in keeping with verruca vulgaris and were designated as BRAF inhibitor associated verrucous keratosis. To our knowledge this represents the first detailed histological analysis of the squamoproliferative lesions which arise in the context of treatment with BRAF inhibitors, and highlights the morphological diversity of these lesions. With the ongoing success of these drugs in clinical trials, these lesions are likely to be more often encountered in routine dermatopathology practice.