Xilio Therapeutics, Inc. announced positive initial data from its Phase 2 clinical trial evaluating vilastobart (XTX101) in combination with atezolizumab for patients with metastatic microsatellite stable colorectal cancer (MSS CRC). The data, presented at the American Society of Clinical Oncology 2025 Gastrointestinal Cancer Symposium, reveal a promising response rate in a heavily pre-treated patient population.
Promising Response in Heavily Pre-treated Patients
The combination therapy demonstrated a 27% preliminary objective response rate (ORR) in patients without liver metastases. These patients had previously undergone multiple lines of anti-cancer therapy. The responses were accompanied by notable decreases in carcinoembryonic antigen (CEA) and circulating tumor DNA (ctDNA) levels, both key tumor biomarkers, as well as improvements in clinical symptoms.
Katarina Luptakova, M.D., Chief Medical Officer of Xilio, emphasized the significance of these findings, stating, "We believe these data highlight the important contribution of vilastobart in this combination, as PD-(L)1 inhibitors alone have demonstrated no meaningful efficacy in patients with MSS CRC to date." She further noted the potential of the combination in tumors resistant to traditional immunotherapy.
Safety and Tolerability
Preliminary safety data indicate that vilastobart has a differentiated safety profile. The incidence of immune-related adverse events (irAEs) was low, with only 5% of patients experiencing colitis. This suggests that vilastobart's tumor-selective design may reduce collateral damage to healthy tissues.
Clinical Trial Details
The Phase 2 trial included 40 patients with metastatic MSS CRC. Patients received vilastobart at a dose of 100 mg once every six weeks (Q6W) and atezolizumab at 1200 mg once every three weeks (Q3W). The median age of the patients was 55 years, and 70% had received three or more prior lines of anti-cancer therapy.
J. Randolph Hecht, M.D., Professor of Clinical Medicine at the David Geffen School of Medicine at UCLA, highlighted the unmet medical need in this patient population, stating, "These preliminary Phase 2 data for the combination of vilastobart and atezolizumab show clear responses for patients with MSS colorectal cancer, an area of very high and increasing unmet medical need."
Future Plans
Xilio Therapeutics plans to report updated data from the Phase 2 trial in mid-2025, including additional response assessments and follow-up data. The company also intends to explore partnership opportunities to broaden the development scope beyond MSS CRC and continue enrollment in Phase 1C dose escalation trials.
The company's overarching goal is to improve patient outcomes in cancer treatment without compromising safety or efficacy. Xilio will host an investor conference to discuss the Phase 2 data and future implications of the combination therapy.
