Abstract 5052: Novel drug resistance mechanisms and drug targets in BRAF mutated peritoneal metastasis from colorectal cancer

Abstract Objective: Patients with peritoneal metastasis (PM) from colorectal cancer (CRC) have inferior prognosis and respond poorly to chemotherapy compared to other metastatic locations. This study aims to identify the molecular explanation for the observed clinical behavior and suggest novel treatment strategies in PM-CRC. Design: Tumor samples from a Norwegian national cohort of 230 patients undergoing surgery and hyperthermic intraperitoneal chemotherapy (HIPEC) with mitomycin C (MMC) for PM-CRC were subjected to targeted DNA sequencing, and associations between molecular findings and clinical data were analyzed. mRNA sequencing was conducted on a subset of thirty samples to compare gene expression in tumors harboring mutations in the BRAF or KRAS oncogenes and wild-type tumors. Results: Almost one-third of the patients had mutations in the BRAF oncogene, which were associated with RNF43/R-Spondin aberrations and low expression of negative Wnt regulators (ligand dependent Wnt activation). This molecular profile, with high abundance in PM, could be an underlying mechanism promoting aggressive tumor biology that facilitates metastasis to the peritoneal cavity, and could contribute to the observed poor overall survival of this patient subgroup. BRAF mutations were also associated with gene expression changes in transport solute carrier proteins and drug metabolism enzymes that could influence the efficacy of MMC and irinotecan, commonly used in PM-CRC treatment. BRAF-mutated tumors exhibited increased expression of BTN immune checkpoint molecules, and targeting these checkpoints in addition to ligand dependent Wnt activation could be two novel targeted therapy approaches. Conclusion: BRAF mutations were associated with particularly poor survival in this cohort, possibly related to altered drug transport and metabolism conferring resistance to MMC and irinotecan. Two potential novel therapeutic approaches were identified, suggesting specific targeting of BTN immune checkpoint molecules and the use of inhibitors to target ligand-dependent Wnt activation. Citation Format: Christin Lund-Andersen, Annette Torgunrud, Chakravarthi Kanduri, Vegar J. Dagenborg, Ida S. Frøysnes, Mette M. Larsen, Ben Davidson, Stein Larsen, Kjersti Flatmark. Novel drug resistance mechanisms and drug targets in BRAF mutated peritoneal metastasis from colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5052.