Xilio Therapeutics announced updated Phase 2 clinical trial data for vilastobart, a tumor-activated anti-CTLA-4 therapy, combined with atezolizumab, in patients with metastatic microsatellite stable colorectal cancer (MSS CRC). The combination showed a 26% objective response rate in heavily pre-treated patients with MSS CRC without liver metastases, with durable responses lasting up to 37 weeks. Furthermore, the treatment demonstrated a favorable safety profile with low incidence of colitis and other immune-related adverse events.
This news is particularly important because MSS CRC is an aggressive cancer type with limited treatment options, especially for those who have progressed after multiple lines of therapy. The observed response rate and duration, combined with the reduced toxicity profile, suggest that vilastobart plus atezolizumab could become a valuable treatment option for these patients. This could address a significant unmet need in a growing patient population.
The Phase 2 trial enrolled 44 heavily pre-treated patients. In those without liver metastases, a 26% objective response rate was observed, including six confirmed partial responses. These responses were accompanied by decreases in tumor biomarkers like circulating tumor DNA and improvements in clinical symptoms. Importantly, the incidence of colitis, a common and serious side effect of anti-CTLA-4 therapies, was low (7%), contributing to the improved tolerability profile. Additionally, a patient with liver metastasis from an earlier Phase 1C trial remains on treatment after over 14 months with a confirmed partial response. Xilio recently initiated enrollment in a new cohort for the Phase 2 trial evaluating a higher dose of vilastobart (150 mg Q6W) and expects to report additional data in the first half of 2026.
These positive results suggest vilastobart has the potential to reshape the treatment landscape for MSS CRC. The combination therapy’s efficacy and safety profile could establish it as a preferred treatment option, potentially improving patient outcomes and quality of life. Xilio is actively pursuing partnerships to further develop and expand the reach of vilastobart, indicating confidence in its potential. Further data from the ongoing trials will be crucial to confirm these promising early findings and determine the optimal dosing strategy.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
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