Abstract 6751: Differences in survival outcomes among metastatic colorectal cancer patients across fibroblast growth factor receptor 2 and 3 expression levels

Abstract Introduction: Fibroblast growth factor receptor 2 and 3 (FGFR2 and FGFR3) are metabolic genes overexpressed in malignant epithelia. In colorectal cancer (CRC), intimate crosstalk between FGFR2/3 and epidermal growth factor receptor (EGFR) pathways has been suggested but is not fully elucidated. As a result, this study investigated associations between FGFR2/3 expression levels and clinical outcomes in patients with metastatic CRC (mCRC) enrolled in the phase III clinical trial CALGB /SWOG 80405. Methods: Data from 433 patients with mCRC enrolled in the CALGB/SWOG 80405 trial were analyzed. Patients received either bevacizumab (bev, n = 226) or cetuximab (cet, n = 207) plus chemotherapy as first-line treatment. Tumor RNA was extracted from FFPE samples and processed through the HiSeq 2500 (Ilumina) platform. Median overall survival (OS) and progression-free survival (PFS) curves were evaluated in all treatment subgroups and stratified according to high (H), medium (M), and low (L) FGFR 2 and 3 gene expression levels. Likelihood ratio tests, hazard ratios (HRs), and 95% confidence intervals (CIs) were calculated using Cox proportional hazards multivariate models, adjusting for age, sex, ECOG performance status, tumor location, number of metastatic sites, KRAS status, consensus molecular subtypes, and treatment arm. Results: Both FGFR2 and FGFR3 expression levels were associated with outcomes in patients treated with cetuximab. FGFR2-L tumors showed significantly longer OS compared to the M (HR = 1.04; 95%CI 0.71-1.51) and H (HR = 1.56; 95%CI 1.06-2.28) expression groups (35.7 vs. 31.2 vs. 23.7 months, p = 0.017). In contrast, FGFR3-L tumors were associated with shorter OS compared to the M (HR = 0.63; 95%CI 0.44-0.92) and H (HR = 0.59; 95%CI 0.41-0.85) expression groups (24.7 vs 32.4 vs 37.1 months, p = 0.0009). Significant differences in PFS were not observed. A nominally significant interaction was found between treatment and FGFR3 expression for both PFS (p = 0.02) and OS (p = 0.0003), but no interaction with FGFR2 expression. No significant associations were detected in patients treated with bev. Neither FGFR2 nor FGFR3 suggested to be prognostic markers after multivariate adjustment analyses. Conclusions: Our findings suggest a predictive role of FGFR3 in patients with mCRC undergoing anti-EGFR treatment. Differences in survival within the cet subgroup suggest that EGFR inhibitor efficacy may be modulated by FGFR2/3 signaling activity. Interestingly, FGFR2 and FGFR3 expressions were inversely and positively correlated with improved OS. The findings suggest that FGFR2 signaling minimizes the specific effects of cetuximab, while FGFR3 signaling amplifies its therapeutic effects. Further studies should determine whether these associations are seen in other anti-EGFR inhibitors and detail the mechanistic interaction between FGFR and EGFR pathways. Citation Format: Steve Soto Trujillo, Yan Yang, Michela Bartolini, Shivani Soni, Pooja Mittal, Fang-Shu Ou, Lesly Torres-Gonzalez, Unnati Hemant Shah, Jae Ho Lo, Yitzhar Goretsky, Wu Zhang, Alan Venook, Sandra Algaze, Joshua Millstein, Heinz-Josef Lenz. Differences in survival outcomes among metastatic colorectal cancer patients across fibroblast growth factor receptor 2 and 3 expression levels 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 6751.