521P - XELOX +bev +tislelizumab for first-line treatment of MSS/pMMR RAS-mutated mCRC: A single-arm, phase II study

Background

First-line single-agent immune checkpoint inhibitors are almost ineffective in patients (pts) with microsatellite-stable (MSS) metastatic colorectal cancer (mCRC). We hope to improve the therapeutic effect by adding immunotherapy to anti-angiogenic therapy combined with chemotherapy in patients with RAS mutations.

Methods

After statistical consideration, increasing the objective response rate (ORR) from 47% to 65% requires enrolling 52 patients. Primary endpoint is ORR of the combination. The treatment combination is applied every 3 weeks as a cycle: Tislelizumab, 200mg, iv, d1; Bevacizumab, 7.5mg/kg, iv, d1; Oxaliplatin, 130mg/㎡, iv, d1; Capecitabine, 1000mg/㎡, bid, po, d1-d14.

Results

As of February 28, 2024, 52 pts were enrolled. The clinical characteristics were shown in the table. Treatment-related adverse events (TRAEs) of any grade occurred in 43 (82.7%) pts. TRAEs of grade ≥ 3 were mainly myelosuppression (5 pts, 9.6%) and Rash (3 pts, 5.8%). There were no fatal TRAEs. ORR was 69.2% (95% CI: 56.3%, 82.2%), Disease control rate (DCR) was 98.1% (95% CI: 94.2%, 100.0%). Until now, no evidence of disease (NED) rate was 15.4% (8 pts, 95% CI: 5.2%, 25.5%). With median follow-up of 8.3 months, 15 pts had progressive disease, median progression free survival (PFS) and overall survival (OS) are not yet mature. Detection biomarkers of drug activity is in progress. Table: 521P

Clinical characteristics