Factors influencing the development of cutaneous squamous cell carcinoma in patients on BRAF inhibitor therapy

Background: BRAF inhibitors (BRAFi) cause paradoxical activation of the MAPK pathway in keratinocytes resulting in cutaneous squamous cell carcinoma (cuSCC). Objective: We sought to examine the clinical factors involved in BRAFi-induced cuSCC development. Methods: We studied 134 patients with BRAF-mutant metastatic melanoma treated with a BRAFi at Westmead Hospital, Sydney, Australia. Details of cuSCC development and associations with melanoma clinicopathologic features and treatment outcome were examined. Results: In all, 32 (24%) patients developed 110 cuSCC after commencing treatment. In all, 61 (55%) cuSCC developed within the first 3 months. Age was the only independent risk factor for cuSCC development. After 3 months of therapy 4% of patients younger than 40 years developed cuSCC compared with 33% who were older than 60 years, and the hazard ratio of developing a cuSCC increased by 1.7 (95% confidence interval 1.3-2.3) per decade (P < .001). BRAFi cuSCC occurred more often in sun-protected areas (42%) compared with sporadic cuSCC (21%) (P < .001). cuSCC was not associated with progression-free survival. Limitations: The study was from a single center and patients were also at risk of sporadic cuSCC. Conclusion: Most BRAFi-induced cuSCC develop within 3 months of BRAFi therapy. The only independent risk factor is increasing age. cuSCC may present in anatomical locations with low ultraviolet exposure such that thorough dermatologic assessment is required.