RAS Mutations Are Associated With the Development of Cutaneous Squamous Cell Tumors in Patients Treated With RAF Inhibitors

Abstract

A B S T R A C TPurpose RAF inhibitors are effective against melanomas with BRAF V600E mutations but may induce keratoacanthomas (KAs) and cutaneous squamous cell carcinomas (cSCCs). The potential of these agents to promote secondary malignancies is concerning. We analyzed cSCC and KA lesions for genetic mutations in an attempt to identify an underlying mechanism for their formation. MethodsFour international centers contributed 237 KA or cSCC tumor samples from patients receiving an RAF inhibitor (either vemurafenib or sorafenib; n ϭ 19) or immunosuppression therapy (n ϭ 53) or tumors that developed spontaneously (n ϭ 165). Each sample was profiled for 396 known somatic mutations across 33 cancer-related genes by using a mass spectrometric-based genotyping platform. ResultsMutations were detected in 16% of tumors (38 of 237), with five tumors harboring two mutations. Mutations in TP53, CDKN2A, HRAS, KRAS, and PIK3CA were previously described in squamous cell tumors. Mutations in MYC, FGFR3, and VHL were identified for the first time. A higher frequency of activating RAS mutations was found in tumors from patients treated with an RAF inhibitor versus populations treated with a non-RAF inhibitor (21.1% v 3.2%; P Ͻ .01), although overall mutation rates between treatment groups were similar (RAF inhibitor, 21.1%; immunosuppression, 18.9%; and spontaneous, 17.6%; P ϭ not significant). Tumor histology (KA v cSCC), tumor site (head and neck v other), patient age (Յ 70 v Ͼ 70 years), and sex had no significant impact on mutation rate or type. ConclusionSquamous cell tumors from patients treated with an RAF inhibitor have a distinct mutational profile that supports a mechanism of therapy-induced tumorigenesis in RAS-primed cells. Conceivably, cotargeting of MEK together with RAF may reduce or prevent formation of these tumors.

Combined BRAF and MEK Inhibition versus BRAF Inhibition Alone in Melanoma

“…However, the types of toxic effects differed. Hyperproliferative cutaneous events, including cutaneous squamous-cell carcinoma and other events related to paradoxical activation of the MAPK pathway, which show the oncogenic potential of BRAF inhibitors, [11][12][13] were significantly abrogated by the addition of the MEK inhibitor trametinib. 12 There were no deaths in either study group that were considered by the investigators to be related to treatment.…”

“…Combined BR AF and MEK Inhibition in Melanoma n engl j med 371;20 nejm.org november 13,2014 1887 receiving monotherapy. There was no significant between-group difference in the frequency of adverse events, including grade 3 and 4 toxic effects.…”

“…[5][6][7] In addition, BRAF-inhibitor-induced paradoxical activation of the MAPK pathway [8][9][10] can result in secondary cancers, including cutaneous squamous-cell carcinoma, and may reactivate RAS-mutant tumors. [11][12][13] Independently, singleagent trametinib, a MEK inhibitor, improves the overall survival of patients with BRAF V600 mutation-positive metastatic melanoma, as compared with chemotherapy, and is not associated with paradoxical activation. 14 The combination of BRAF and MEK inhibition, as compared with single-agent BRAF inhibition, delayed the emergence of resistance and decreased the incidence of cutaneous hyperproliferative lesions in preclinical models.…”

Single-molecule superresolution imaging allows quantitative analysis of RAF multimer formation and signaling

“…Mutations of these residues (e.g., R509H in BRAF and, equivalently, R401H in CRAF) profoundly diminished dimerization and kinase activity of RAF (11)(12)(13). Recently, dimerization also was implicated in RAFimediated activation of RAF in BRAF WT tumors (12,13), in acquired resistance of BRAF V600E tumors to RAFi (14), and in the development of RAFi-induced secondary squamous carcinomas (10).…”

“…Moreover, BRAF mutant melanomas that are initially sensitive to RAFi rapidly become resistant by using a variety of compensatory mechanisms including RAF isoform switching and activation of other pathways including RTKs, RAS, or PI3K (9). In addition, some RAFis (e.g., vemurafenib) accelerate the occurrence of secondary squamous cell carcinomas (10).…”