Response of BRAF inhibitor-associated squamous cell lung carcinoma to drug withdrawal.

Vemurafenib and dabrafenib, two Food and Drug Administration-approved selective BRAF kinase inhibitors (BRAFi), have revolutionized the targeted therapy of cutaneous melanoma. Off-target effects of these drugs paradoxically activate the MAP kinase pathway in BRAF wild-type cells, leading to secondary malignancies. Although cutaneous squamous cell carcinomas are by far the most frequent, emergence of potentially life-threatening secondary tumors from other sites following prolonged therapy is a growing concern. Herein, we provide the first case report of squamous cell lung carcinoma apparently secondary to BRAFi developing in a metastatic melanoma patient on vemurafenib for 23 months. Subsequent BRAFi with dabrafenib for 5 months was accompanied by rapid lung cancer progression with 86% increase in diameter. Withdrawal of BRAFi as the only change in therapy resulted in partial response maintained for more than 8 months. Clinicians should be atuned to the risk of noncutaneous second malignancies induced by BRAFi, particularly in the setting of progression of an isolated lesion after prolonged therapy.