• Fei Su, Amaya Viros, Carla Milagre, Kerstin Trunzer, Gideon Bollag, Olivia Spleiss, Jorge S Reis-Filho, Xiangju Kong, Richard C Koya, Keith T Flaherty, Paul B Chapman, Min Jung Kim, Robert Hayward, Matthew Martin, Hong Yang, Qiongqing Wang, Holly Hilton, Julie S Hang, Johannes Noe, Maryou Lambros, Felipe Geyer, Nathalie Dhomen, Ion Niculescu-Duvaz, Alfonso Zambon, Dan Niculescu-Duvaz, Natasha Preece, Lídia Robert, Nicholas J Otte, Stephen Mok, Damien Kee, Yan Ma, Chao Zhang, Gaston Habets, Elizabeth A Burton, Bernice Wong, Hoa Nguyen, Mark Kockx, Luc Andries, Brian Lestini, Keith B Nolop, Richard J Lee, Andrew K Joe, James L Troy, Rene Gonzalez, Thomas E Hutson, Igor Puzanov, Bartosz Chmielowski, Caroline J Springer, Grant A McArthur, Jeffrey A Sosman, Roger S Lo, Antoni Ribas, and Richard Marais.
• Hoffmann-La Roche, Nutley, NJ, USA.
• N. Engl. J. Med. 2012 Jan 19; 366 (3): 207215207-15.

BackgroundCutaneous squamous-cell carcinomas and keratoacanthomas are common findings in patients treated with BRAF inhibitors.MethodsWe performed a molecular analysis to identify oncogenic mutations (HRAS, KRAS, NRAS, CDKN2A, and TP53) in the lesions from patients treated with the BRAF inhibitor vemurafenib. An analysis of an independent validation set and functional studies with BRAF inhibitors in the presence of the prevalent RAS mutation was also performed.ResultsAmong 21 tumor samples, 13 had RAS mutations (12 in HRAS). In a validation set of 14 samples, 8 had RAS mutations (4 in HRAS). Thus, 60% (21 of 35) of the specimens harbored RAS mutations, the most prevalent being HRAS Q61L. Increased proliferation of HRAS Q61L-mutant cell lines exposed to vemurafenib was associated with mitogen-activated protein kinase (MAPK)-pathway signaling and activation of ERK-mediated transcription. In a mouse model of HRAS Q61L-mediated skin carcinogenesis, the vemurafenib analogue PLX4720 was not an initiator or a promoter of carcinogenesis but accelerated growth of the lesions harboring HRAS mutations, and this growth was blocked by concomitant treatment with a MEK inhibitor.ConclusionsMutations in RAS, particularly HRAS, are frequent in cutaneous squamous-cell carcinomas and keratoacanthomas that develop in patients treated with vemurafenib. The molecular mechanism is consistent with the paradoxical activation of MAPK signaling and leads to accelerated growth of these lesions. (Funded by Hoffmann-La Roche and others; ClinicalTrials.gov numbers, NCT00405587, NCT00949702, NCT01001299, and NCT01006980.).

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