Background: For adequately treated patients (pts) with advanced colorectal cancer, the current third-line treatment standard of TKIs or TAS-102 administration has a low clinical objective response rate and its effectiveness seems to be limited. Preclinical studies have suggested that EGFR pathway blockage and immune checkpoint inhibition have synergistic therapeutic effects in these pts. The purpose of this study was to examine the efficacy and safety of tislelizumab (anti-PD-1 antibody) plus cetuximab and irinotecan in pts with previously treated RAS wild-type advanced colorectal cancer. Methods: This is an open-label, single-arm, phase II study. RAS wild-type advanced colorectal cancer pts with at least two previous lines of therapy were included in this study and administered with tislelizumab plus cetuximab and irinotecan until disease progression or intolerable toxicity. The primary endpoint was objective response rate (ORR) (RESCIT 1.1). Secondary endpoints included DCR, PFS, OS and safety. Results: In total, 35 eligible RAS wild-type advanced colorectal cancer pts were enrolled from March 2021 to September 2021. The median age was 58 years. All 35 pts were identified as BRAF/RAS wild-type, and 33 (94%) had left-sided colon cancer. The percentages of pts with second-line, third-line and ≥fourth-line previous treatments were 37%, 49%, and 14%, respectively. Thirty-four pts (97%) had received targeted therapies previously, including 29 (83%) with anti-EGFR therapy. By Aug 17th, 2022, 2 pts had withdrawn from the study for personal reasons, and the remaining 33 pts were evaluated for efficacy. Twelve of the 33 (36.4%) pts achieved clinical partial remission and 14 (42.4%) achieved stable disease; disease progression occurred in 6 pts and 1 patient died. The unconfirmed ORR was 36.4% and the DCR was 78.8%. The confirmed ORR was 33.3%. Until Aug 17th, 2022, 1 pts continued treatments. The median PFS was 6.83 months. Among the 33 treated pts, 32 (97.0%) had treatment-related adverse events (AEs). Common AEs included rash (n=32), fatigue (n=30), decreased appetite (n=30), nausea (n=28), diarrhea (n=16), vomiting (n=14), liver dysfunction (n=13), leukopenia (n=12) anemia(n=10), neutropenia (n=9), paronychia (n=8), oral mucositis (n=4), and thrombocytopenia (n=4). Three (9.1%) of the 33 pts reported grade ≥3 AEs, including rash (n=1), neutropenia (n=2). Conclusions: Tislelizumab plus cetuximab and irinotecan showed an encouraging clinical efficacy and tolerable safety in previously treated pts with RAS wild-type advanced colorectal cancer. Clinical trial information: NCT05143099.