Abstract 3264: Characterization of EGFR ectodomain mutation in acquired resistance to cetuximab in colorectal cancer

Abstract Colorectal cancer (CRC) remains the second leading cause of cancer-related deaths in the United States (US). Individuals with surgically unresectable stage four CRC have a five-year overall survival rate of 13%. Targeting of the receptor tyrosine kinase (RTK), EGF receptor (EGFR) with therapeutic monoclonal antibodies (cetuximab, panitumumab) is approved for use in wild-type (WT) KRAS/NRAS/BRAF (RAS/RAF) advanced CRC. However, these antibodies as a single agent have response rates of 12-17% and expected progression-free survivals of only 3-4 months. Accordingly, resistance may be present at the outset (de novo resistance) or develop during treatment (acquired resistance). Here, we report the identification of an EGFR ectodomain missense mutation acquired in vitro in response to treatment with anti-epidermal growth factor receptor (EGFR) antibody cetuximab. Using 2D and 3D drug sensitivity assays, our results demonstrate that this EGFR ectodomain mutation in addition to being resistant to cetuximab and panitumumab, also could not be targeted by the oligoclonal antibody cocktail MM-151. To determine whether this EGFR ectodomain mutation is necessary and sufficient to impart cetuximab resistance, we engineered CRC lines to inducibly overexpress mutant EGFR and showed that this was sufficient to induce cetuximab resistance. Further structural, and functional characterization is underway for this ectodomain mutation that confers resistance to cetuximab and will be shared during the meeting. These findings necessitate the need for additional treatment strategies for a subset of subjects with mCRC who do not respond to treatment with cetuximab/panitumumab and MM-151. Citation Format: Neeraj Joshi, Ramona Graves Deal, Galina Bogatcheva, James N. Higginbotham, Marisol Ramirez, Benjamin P. Brown, Qi Liu, Jens Meiler, Bhuminder Singh. Characterization of EGFR ectodomain mutation in acquired resistance to cetuximab in 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 3264.