Abstract 5099: Prevalence of fibroblast growth factor receptor (FGFR) alterations (alts) and programmed death-ligand 1 (PD-L1) expression (exp) in Chinese solid tumor patients (pts)

Abstract Background: PD-L1 expression drives anti-PD (L) -1 treatment decisions across many cancer indications. FGFR inhibitors have been approved for the treatment of metastatic urothelial cancer (UC) and cholangiocarcinoma with FGFR alts. BALVERSA (erdafitinib), a selective pan-FGFR kinase inhibitor, has shown clinical activity against FGFR altered solid tumors in pts who exhausted standard treatment options. It is important to understand the prevalence of FGFR alts and relationship between FGFR alts and PD-L1 expression levels in different cancer types. Methods: In this real-world study, 9937 Chinese solid tumor pts with the PD-L1 (22C3) immunohistochemistry and OrigiMed 450-gene next-generation sequencing panel results were selected. Chi-square test and Fisher test were used to explore the association between the FGFR alts and PD-L1 expression. Results: FGFR1-4 somatic alts were found in 9. 0% of Chinese cancer pts evaluated. FGFR1 amplification (amp) was the most prevalent alts identified (1. 9%). There were no significant differences in frequency of FGFR alts between the Chinese cohort and MSK-IMPACT cohort in each cancer type tested. Up to 40. 6% of pts evaluated were PD-L1 positive (CPS ≥1 or TPS ≥1%). The PD-L1 positive rate (TPS ≥1%) in SCLC (12. 4%, n=121) and NSCLC adenocarcinoma tumors (LUAD) (26. 1%, n=2902) was relatively low. In few tumor types, higher expression of PD-L1 in FGFR altered samples was observed compared with FGFR unaltered samples in pan-tumor (mean TPS 14. 8% vs. 8. 6%, P=6. 0*E-9; mean CPS 6. 3 vs. 6. 1, P=3*E-4). Those includes LUAD (mean TPS 14. 2% vs. 7. 4%, P = 1. 7*E-16), colorectal tumor (mean CPS 4. 6 vs. 3. 9, P = 4. 6*E-8), and uterine tumor (mean CPS 8. 1 vs. 6. 5, P = 9. 6*E-5). While PD-L1 expression is lower in FGFR altered samples than FGFR unaltered samples in UC (n=154; mean CPS 3. 9 vs. 6. 8, P = 0. 004). No relationship was observed between FGFR alts and PD-L1 expression in cholangiocarcinoma (n=610). Specific FGFR alts eligible for erdafitinib UC treatment were further investigated in UC and observed with rate 10. 4%, including FGFR3 short variants (9. 7%) as main alts. Specific FGFR altered tumors showed similar trend with lower PD-L1 expression than FGFR unaltered tumors in UC. The inverse relationship between FGFR alts and PD-L1 expression in UC compared to other solid tumors may explain variable role of FGFRs since the predominant FGFR alt types vary among different cancer types (FGFR3 short variants enriched in UC vs no such predominant FGFR alt types in other cancer types). Conclusion: The large Chinese solid tumor cohort analysis showed comparable FGFR alts prevalence between Chinese and Western population. Differences in relationship between FGFR alts and PD-L1 expression across tumor types reflect the differential role of predominant FGFR types in each tumor type. Citation Format: Min Qing, Fei Yang, Xiaowei Chen, Xuesong Lyu, Aodi Wang, Yanfei Yu, Shibu Thomas, Longen Zhou. Prevalence of fibroblast growth factor receptor (FGFR) alterations (alts) and programmed death-ligand 1 (PD-L1) expression (exp) in Chinese solid tumor patients (pts) 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 5099.