4634 - Comparative molecular analyses between microsatellite stable BRAFV600E mutant colorectal cancers and BRAFV600E mutant melanomas.

Background

Several studies in BRAF^V600E colorectal cancers (CRC) have failed to replicate the efficacy of BRAF inhibitors in treatment of BRAF^V600E melanomas (Mel), suggesting the existence of different resistance mechanisms as well as molecular and biological differences between the 2 tumor types. Herein, we examine these differences.

Methods

Tumor samples submitted to Caris Life Sciences for NGS DNA sequencing (592 gene panel) and RNA sequencing (54 gene panel) between the years 2015 and 2019 were retrospectively studied. Only microsatellite stable (MSS) tumors with either BRAF^V600E mutation or wild type (WT) BRAF status were included in this initial analysis. Chi-square tests determined differences.

Results

A total of 8409 tumor samples were analyzed: CRC (N = 7453: BRAF^V600E=373; WT = 7080) and Mel samples (N = 956: BRAF^V600E=274; WT = 682). The most frequently mutated genes in BRAF^V600E CRC were TP53 (81%), APC (26%), and SMAD4 (22.4%), compared to CDKN2A (22%), PTEN (13%), and TP53 (13%) in BRAF^V600E Mel. Molecular alterations that are significantly more frequent in BRAF^V600E CRC vs BRAF^V600E Mel but not significantly different between BRAF WT CRC vs BRAF WT Mel included RSPO3 fusions (CRC=22.6% vs Mel=0%, P = 0.027); RNF43 deletions (2.0% vs 0%, p = 0.019); and mutations in RNF43 (18.8% vs 0%, P < 0.001), AKT1 (3.5% vs 0.4%, p = 0.008), and MTOR (2.4% vs 0.4%, p = 0.037). RSPO3 fusions and RNF43 mutations/deletions are mutually exclusive. Significantly more frequent alterations in BRAF^V600E Mel compared to BRAF^V600E CRC (but not in either WT) included deletions in PTEN (7% vs 3%, p = 0.005) and mutations in PTEN (12.9% vs 5.4%), MITF (1.9% vs 0%), STK11 (1.5% vs 0%), ERCC2 (1.1% vs 0%), FANCC (1.2% vs 0%), and CDK4 (1.5% vs 0%) (p < 0.05 for all).

Conclusions

BRAF^V600E CRC carry molecular alterations that are distinct from BRAF^V600E Mel. RSPO3 fusions and RNF43 alterations are prevalent in BRAF^V600E CRC tumors in a mutually exclusive manner, suggesting that Wnt pathway activation via genetic alterations in upstream Wnt pathway regulators may play an important role in BRAF^V600E CRC tumorigenesis and resistance to BRAF inhibitors. Drug combinations that target both the MAPK and Wnt pathways may warrant further investigation.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

M.E. Salem: Travel / Accommodation / Expenses: Caris Life Sciences. J. Xiu: Full / Part-time employment: Caris Life Sciences. A. Grothey: Travel / Accommodation / Expenses: Caris Life Sciences. R.M. Goldberg: Research grant / Funding (self), Travel / Accommodation / Expenses: Caris Life Sciences. Z. Gatalica: Full / Part-time employment: Caris Life Sciences. R. Feldman: Full / Part-time employment: Caris Life Sciences. M. Saul: Full / Part-time employment: Caris Life Sciences. W..M. Korn: Full / Part-time employment: Caris Life Sciences. A.F. Shields: Research grant / Funding (institution), Travel / Accommodation / Expenses: Caris Life Sciences. J.L. Marshall: Advisory / Consultancy: Caris Life Sciences. H.J. Lenz: Travel / Accommodation / Expenses: Caris Life Sciences. All other authors have declared no conflicts of interest.