AUS
NZ
UK
CA
USA
IND
Highlights
- 27% preliminary response rate observed in metastatic microsatellite stable colorectal cancer (MSS CRC) without liver metastases.
- Combination of vilastobart (XTX101) and atezolizumab shows favorable safety profile with low immune-related adverse events.
- Xilio plans to expand beyond MSS CRC, with updated Phase 2 data expected in mid-2025.
Xilio Therapeutics (Nasdaq:XLO) has announced promising initial Phase 2 data for vilastobart (XTX101), in combination with atezolizumab, as a treatment for metastatic microsatellite stable colorectal cancer (MSS CRC). The trial's preliminary results demonstrate that the combination therapy offers significant potential for patients, particularly those without liver metastases, showing a 27% preliminary response rate.
Key Trial Findings
The Phase 2 trial involved 40 patients with metastatic MSS CRC, and initial results suggest that the combination of vilastobart and atezolizumab may offer substantial clinical benefit. Of particular note, 27% of patients without liver metastases showed a positive response to the treatment, including three partial responses, two of which were confirmed. These patients experienced tumor size reductions of 47% and 57%, highlighting the potential of this combination to improve outcomes for this difficult-to-treat patient group.
Additionally, the trial observed decreased levels of carcinoembryonic antigen (CEA) and circulating tumor DNA (ctDNA), markers often associated with disease progression, suggesting that the combination therapy may be effectively targeting tumor cells. Furthermore, the combination demonstrated a positive impact on clinical symptoms, further supporting its potential as an effective treatment option for MSS CRC.
Safety Profile and Tolerability
Safety data from the trial was also encouraging, with the combination treatment demonstrating a favorable safety profile. Immune-related adverse events were low, with only 5% of patients experiencing colitis, a common side effect associated with immunotherapy. This is a positive indicator that vilastobart combined with atezolizumab may be better tolerated compared to other therapies, with a low risk of serious immune-mediated toxicity. Importantly, the trial also showed that 23 patients were still receiving treatment as of the data cutoff, underscoring the durability of the response in a significant portion of patients.
Response Rate and Disease Control
Among the 18 patients evaluable for response, 11 patients without liver metastases experienced promising results, with a disease control rate of 55%. This indicates that the combination therapy not only shrinks tumors in some patients but also helps to stabilize disease progression in others, further supporting its potential as an effective treatment option for MSS CRC.
Challenges and Future Plans
While the trial showed promising results in patients without liver metastases, the efficacy in patients with liver metastases was less robust, with only a 14% disease control rate observed in this group. Additionally, three patients discontinued treatment due to adverse events, and six patients experienced Grade 3 or 4 treatment-related adverse events, highlighting the need for further investigation into optimizing the therapy's safety and efficacy profile across different patient populations.
Despite these challenges, Xilio is optimistic about the potential of vilastobart in combination with atezolizumab and plans to report updated Phase 2 data in mid-2025. The company is also exploring partnership opportunities to expand the development of vilastobart beyond MSS CRC, potentially targeting other cancer types where this combination could show promise.
