Tumor vascularity as a predictor of FGFR inhibitor response in FGFR2-fused intrahepatic cholangiocarcinoma.

638 Background: Fibroblast growth factor receptor 2 (FGFR2) fusion is a well-established mutation in intrahepatic cholangiocarcinoma (iCCA), accounting for approximately 10% of cases. Current treatments, including pemigatinib, infigratinib, and futibatinib, have shown promising results with response rates of less than 40%. Most patients experience progression within 6-8 months, and reliable biomarkers to predict treatment response are still lacking. This study aimed to assess the clinical outcomes of FGFR inhibitors in patients (pts) with FGFR2-fused iCCA, while investigating tumor vascularity as a potential predictor of treatment efficacy. Methods: We retrospectively analyzed data from 134 pts treated at MD Anderson Cancer Center between 2009 and 2024, focusing on 73 pts with comprehensive clinical data. The cohort included pts treated with futibatinib (n=16), infigratinib (n=16), pemigatinib (n=36), and derazantinib (n=5). Tumor vascularity was assessed via Hounsfield units (HU) from CT images, including a mathematical parameter to calculate a ratio of hypervascular tumor rim thickness to tumor diameter. Transcriptomic analysis of 11 pts was performed to explore mRNA expression related to tumor vasculature. Kaplan-Meier analysis for progression-free survival (PFS) and ANOVA for statistical comparisons were applied. Results: The median age was 60 years, and 41 pts were female. For FGFR2-fused iCCA, median PFS for first-line gemcitabine-based chemotherapy with or without immunotherapy was 4.07 months [3.0-5.1]. Among FGFR inhibitors, mPFS was 7.07 months [95% CI: 5.10-8.16], with no significant difference in outcomes between FGFR inhibitors. 59 pts had comparable CT images and were grouped into 3 groups based on K-means clustering: Group 1 (n=30) had mPFS of 3.07 months [2.03-4.10]; Group 2 (n=22), mPFS of 9.10 months [8.2-11.2]; Group 3 (n=7), mPFS of 34.03 months [18.2-37.6]. Group 1 had the most hypovascular tumors (the lowest HU in the periphery of tumors), while Group 3 had the most hypervascular tumors (p=0.017). The HU ratio of the hypervascular tumor rim thickness to tumor diameter showed a trend, with the highest ratio in Group 3 and the lowest in Group 1 (p=0.09). Transcriptomic analysis revealed a trend toward higher VEGF/VEGFR gene expression in hypervascular tumors. Eight pts received second-line FGFR inhibitors, with mPFS of 5.0 months [2.1-8.3]. Conclusions: Pts with FGFR2-fused iCCA have a shorter PFS on first-line chemotherapy, and PFS outcomes for FGFR inhibitors were consistent with existing data. Tumor vascularity, as assessed by CT imaging, may be a valuable predictor of response to FGFR inhibitors. This study suggests that hypervascular tumors may have better outcomes, warranting further investigation in a larger cohort to confirm these findings and establish tumor vascularity as a predictive biomarker for FGFR inhibitor therapy.