RAS mutations are associated with the development of cutaneous squamous cell tumors in patients treated with RAF inhibitors

Abstract

Purpose: 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.

Methods: Four international centers contributed 237 KA or cSCC tumor samples from patients receiving an RAF inhibitor (either vemurafenib or sorafenib; n = 19) or immunosuppression therapy (n = 53) or tumors that developed spontaneously (n = 165). Each sample was profiled for 396 known somatic mutations across 33 cancer-related genes by using a mass spectrometric-based genotyping platform.

Results: Mutations 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 < .01), although overall mutation rates between treatment groups were similar (RAF inhibitor, 21.1%; immunosuppression, 18.9%; and spontaneous, 17.6%; P = not significant). Tumor histology (KA v cSCC), tumor site (head and neck v other), patient age (≤ 70 v > 70 years), and sex had no significant impact on mutation rate or type.

Conclusion: Squamous 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.

Fig 1.

Mutually exclusive and co-occurring mutations in human squamous cell tumors. Each column describes an individual sample with a detected mutation. Affected genes are listed in rows, with single mutations indicated by black bars and co-occurring mutations indicated by red bars. Histology (cutaneous squamous cell carcinoma [cSCC] and keratoacanthoma [KA]) and treatment cohort (RAF-inhibitor, gold; immunosuppressed, gray; spontaneous, blue) are detailed on the bottom two rows.

Fig A1.

Tumor samples with BRAF V600E mutations demonstrating colocalized cutaneous squamous cell tumors and melanoma. (A) Sample 3: hematoxylin and eosin (H+E) stain demonstrating classical keratoacanthoma histology, with an interspersed S100-positive melanocytic population. (B) Low-power and (C) high-power images of H+E stains from sample 39. AE1/AE3-positive cells (squamous cell carcinoma) are demonstrated immediately adjacent to S100-positive and melan-A–positive cells (melanoma).