Preliminary safety and efficacy of upfront FOLFOXIRI and bevacizumab with cadonilimab in patients with proficient mismatch repair/microsatellite stable (pMMR/MSS) metastatic colorectal cancer: A multicenter phase II study (SYLT-026).

198 Background: The AtezoTRIBE phase II trial reported that adding Atezolizumab to upfront FOLFOXIRI plus Bevacizumab significantly improved overall survival (OS) in patients with metastatic colorectal cancer (mCRC). However, the improvement in OS was modest within the pMMR/MSS subgroup (HR, 0.80 [80% CI, 0.63–1.02]; P = 0.117) [1]. Cadonilimab, a humanized bispecific antibody targeting both PD-1 and CTLA-4, may offer enhanced therapeutic benefits. Therefore, this study aims to investigate whether the addition of Cadonilimab to upfront FOLFOXIRI plus Bevacizumab improves efficacy while maintaining safety in patients with pMMR/MSS mCRC. Methods: This multicenter, single-arm phase II study enrolled treatment-naive patients with pMMR/MSS mCRC, aged 18–75, who had at least one measurable lesion according to RECIST 1.1, an ECOG performance status (PS) of 0–2, and adequate organ function. Patients with dMMR/MSI-H tumors or prior immunotherapy were excluded. Eligible participants received FOLFOXIRI (irinotecan 165 mg/m², oxaliplatin 85 mg/m², leucovorin 200 mg/m², and fluorouracil 2400 mg/m² as a 48-hour infusion), along with Bevacizumab (5 mg/kg), and Cadonilimab (6 mg/kg). Treatment was administered for up to twelve 14-day cycles, followed by maintenance therapy with fluoropyrimidine and Bevacizumab plus Cadonilimab for up to 52 weeks, or until disease progression, unacceptable toxicity, or withdrawal of consent. Patients were equally enrolled, with 10 having liver metastases and 10 without. The primary endpoint was objective response rate (ORR) per RECIST 1.1. Results: As of August 30, 2024, 20 patients were enrolled, with a median age of 65.5 years (range: 33–74). Of these, 40% had an ECOG PS of 1 or 2, 55% had three or more metastatic organs, and 7 patients (35%) had RAS or BRAF mutations. The median follow-up was 5.0 months. Fifteen patients underwent at least two imaging assessments, revealing a confirmed ORR of 100% (15/15) and a disease control rate (DCR) of 100%. The median progression-free survival (PFS) and OS data were not yet mature. All 20 patients experienced treatment-emergent adverse events, most of which were grade 1 or 2. One patient (5%) discontinued treatment due to immune-mediated colitis. The most common grade 3/4 adverse events included neutropenia (55%), leukopenia (15%), infusion reactions (5%), dermatitis (5%), colitis (5%), anemia (5%), elevated ALT (5%), and diarrhea (5%). No new safety signals were identified. Conclusions: In conclusion, Cadonilimab in combination with FOLFOXIRI and Bevacizumab demonstrated promising efficacy and a manageable safety profile as a first-line treatment for patients with pMMR/MSS mCRC. Further investigation in larger trials is warranted. 1. Antoniotti, et al, J Clin Oncol, 2024. Clinical trial information: NCT05839470 .