Efficacy, safety and DNA methylation analysis of cadonilimab combined with taxane and cisplatin as first-line treatment for advanced esophageal squamous cell carcinoma (ESCC): Updated results from an open-label, multicenter phase II trial (AK104-IIT-

463 Background: Immune checkpoint inhibitors combined with chemotherapy had become the first-line standard treatment for advanced ESCC and cadonilimab, as a bispecific antibody simultaneously targeting PD-1 and CTLA-4, may further boost anti-tumor activity with a satisfied safety profile. Here, we present the updated data for the safety and efficacy of cadonilimab combination therapy as the first-line treatment in advanced ESCC. The correlation between DNA methylation and clinical response was also investigated. Methods: Treatment-naïve patients (pts) with unresectable locally advanced or metastatic ESCC were enrolled. Cadonilimab (10mg/kg, iv, d1, q3w) combined with paclitaxel or nab-paclitaxel (175 mg/m 2 , iv, d1, q3w) and cisplatin (65 to 75 mg/m 2 , iv, d1, q3w) were administrated for up to 6 cycles, then Cadonilimab (10mg/kg, iv, d1, q3w) monotherapy continued as maintenance until progressive disease or unacceptable toxicity, with a maximum of 24 months. The primary endpoint was objective response rate (ORR). Secondary endpoints were progression-free survival (PFS), overall survival (OS), disease control rate (DCR) and safety. Plasma cell-free DNA samples were collected before and after treatment and prepared for methylation level sequencing. Results: As of September 20, 2024, 43 pts were enrolled with a median age of 61 years (range 44-75), 81.4% were male, 39.5% had PD-L1 CPS≥10 and 95.3% had metastatic diseases. All pts were evaluable for safety and efficacy. The ORR was 81.4% (95%Cl: 66.1%-91.1%) and DCR was 97.7% (95%Cl: 86.2%-99.9%). The median PFS (mPFS) was 7.05 months (mo) (95%Cl: 5.86-8.24) and OS analysis was immature. In the PD-L1 CPS≥10 pts, the ORR was 100.0% (95%Cl: 77.1%-100.0%) and mPFS was 7.05 mo (95%Cl: 5.19-8.91). In the PD-L1 CPS＜10 pts, the ORR was 77.3% (95%Cl: 54.2%-91.3%) and mPFS was 7.05 mo (95%Cl: 5.87-8.24). Six hyper-methylated CpG sites, EPTIN9、PKNOX2、DLEU7、SOX7、CNRIP1 and LINC00554 might be the candidate biomarkers as the mean pretreatment methylation levels were significantly higher in the PR pts than those in the non-PR pts (p=7.8×10 -7 ). Grade 3-4 treatment-related adverse events (TRAEs) were reported in 44.2% (19/43) pts, mainly including neutropenia (25.6%), leukopenia (9.3%) and hyponatremia (7.0%). The infusion-related reactions (IRR) occurred in 14.0% (6/43) and grade ≥3 IRR occurred in 4.7% (2/43) pts. 7 pts discontinued cadonilimab administration due to TRAEs. Conclusions: The updated results suggested that bispecific antibody cadonilimab combined with taxane and cisplatin as first-line treatment continued to show encouraging anti-tumor activity and manageable safety in pts with advanced ESCC. DNA methylation level might be a potential biomarker for guiding patient outcomes. Clinical trial information: NCT05522894 .