Abstract 1570: Preclinical assessment of EGFR and checkpoint inhibitor combination therapy in spontaneous colon cancer model

Abstract Spontaneous colon cancer models closely mimic human disease, enabling translational research and therapeutic evaluation. The ApcMin/+ mouse, with a mutation in the APC gene, is a well-established model for intestinal neoplasia. In recent years, immunotherapy has shown promise in colorectal cancer, the combination of EGFR inhibitors and immune checkpoint blockers remains underexplored in polyp models. This research looks at how well these two treatments work together in stopping early tumors, using real time colonoscopy to watch how tumors grow in APC mice. In this study we have evaluated the preclinical efficacy of immune checkpoint inhibitors (anti-PD-1/ CTLA-4) and EGFR inhibitors like Erlotinib and as standalone and in combination regimen in spontaneous colon cancer model of C57BL/6J-ApcMin/J mice. Four-week-old mice were randomized, and treatment was initiated with anti-PD1 10mg/kg, i.e., BIW for 8 weeks, anti-CTLA-4 dosed at 10mg/kg, i.p; BIW for 8 weeks and Erlotinib 50mg/kg, po; QD for 8 weeks, as standalone and combination with Erlotinib. Weekly colonoscopies with image capture tracked tumor progression. Body weight, clinical signs, and mortality were monitored biweekly. At the study end, mice were euthanized, and their small intestines and colons were collected, imaged, and assessed for polyp load using ImageJ software. Colon samples were rolled and processed for histological analysis. In the current spontaneous colon cancer model, endoscopy assessment revealed that the anti-PD-1, CTLA-4, and Erlotinib monotherapies significantly reduced lesions, tumor burden, inflammation, and polyp area compared to controls. Significantly reduced the total area of intestinal polyps relative to the control group. The percentage (%) reduction in polyp area in the small intestine (proximal, middle, and distal) and colon was found to be 38%, 27%, and 68% respectively. However, the combination of Erlotinib with anti-PD-1 and anti-CTLA-4 antibodies showed a substantial reduction in colonic tumor burden. The % reduction in polyp area in the small intestine (proximal, middle, distal) and colon was found to be 88% and 74%, respectively. Histology showed less inflammation and dysplasia in the combination group versus monotherapy. In summary, combination therapy led to a marked decrease in both the number and size of small intestinal polyps in ApcMin/+ mice, with potential survival benefits. These findings indicate that dual targeting of EGFR signalling and immune checkpoints may enhance antitumor efficacy, presenting a promising approach for colorectal cancer treatment Citation Format: Balaji Ramachandran, Satheeshkumar Rajendiran, Girish Joshi, Krishnappa Haladasappa, . Preclinical assessment of EGFR and checkpoint inhibitor combination therapy in spontaneous colon cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1570.