Skin Tumors Induced by Sorafenib; Paradoxic RAS–RAF Pathway Activation and Oncogenic Mutations of HRAS, TP53, and TGFBR1

Purpose: The emergence of skin tumors in patients treated with sorafenib or with more recent BRAF inhibitorsisanintriguingandpotentiallyseriousevent.Wecarriedoutaclinical,pathologic,andmolecular study of skin lesions occurring in patients receiving sorafenib. Experimental Design: Thirty-one skin lesions from patients receiving sorafenib were characterized clinically and pathologically. DNA extracted from the lesions was screened for mutation hot spots ofHRAS, NRAS, KiRAS, TP53, EGFR, BRAF, AKT1, PI3KCA, TGFBR1, and PTEN. Biological effect of sorafenib was studied in vivo in normal skin specimen and in vitro on cultured keratinocytes. Results: We observed a continuous spectrum of lesions: from benign to more inflammatory and proliferative lesions, all seemingly initiated in the hair follicles. Eight oncogenic HRAS, TGFBR1, and TP53 mutationswerefoundin2benignlesions,3keratoacanthomas(KA)and3KA-likesquamouscellcarcinoma (SCC). Six of them correspond to the typical UV signature. Treatment with sorafenib led to an increased keratinocyte proliferation and a tendency toward increased mitogen-activated protein kinase (MAPK) pathway activation in normal skin. Sorafenib induced BRAF‐CRAF dimerization in cultured keratinocytes and activated CRAF with a dosedependent effect on MAP-kinase pathway activation and on keratinocyte proliferation. Conclusion: Sorafenib induces keratinocyte proliferation in vivo and a time- and dose-dependent activation of the MAP kinase pathway in vitro. It is associated with a spectrum of lesions ranging from benignfollicularcysticlesionstoKA-likeSCC.Additionalandpotentiallypreexistingsomaticgeneticevents, like UV-induced mutations, might influence the evolution of benign lesions to more proliferative and malignant tumors. Clin Cancer Res; 18(1); 263–72. � 2011 AACR.