Xilio Therapeutics disclosed that its Phase 2 study of vilastobart, a tumor‑activated anti‑CTLA‑4 antibody, achieved a 40 % objective response rate in heavily pre‑treated patients with microsatellite stable metastatic colorectal cancer (MSS mCRC) who had high plasma tumor‑mutational burden (TMB) and no liver metastases. The data were presented as a late‑breaking poster at the Society for Immunotherapy of Cancer (SITC) 40th Annual Meeting on November 7, 2025.
The 40 % response rate is striking because MSS mCRC has historically shown poor activity to checkpoint inhibitors, with typical response rates below 10 %. By demonstrating a markedly higher rate in a biomarker‑selected cohort, the study suggests that plasma‑based TMB can serve as a predictive marker for vilastobart. This finding could broaden the treatable population for a drug that has yet to receive regulatory approval and positions Xilio to pursue a partnership to accelerate development and commercialization.
Chief Medical Officer Katarina Luptakova highlighted the correlation between plasma TMB and response, noting that the data “demonstrated a statistically significant association between high plasma TMB and objective responses.” The company is actively seeking a partner to advance vilastobart, indicating that the positive data may open new collaboration opportunities and accelerate the drug’s path to market.
Financially, Xilio reported a Q2 2025 earnings per share of –$0.16, missing consensus estimates of –$0.08, while revenue of $8.21 million met expectations. The company’s cash runway extends through Q3 2026, providing a buffer for continued clinical development and potential partnership negotiations.
Over the past six months, Xilio’s stock has risen 24.77 %, reflecting investor confidence in the company’s pipeline and the recent clinical data. While the announcement itself did not trigger an immediate market reaction, the strong response rate and biomarker validation are likely to influence future partnership discussions and investor sentiment.
The results underscore the importance of precision oncology and suggest that vilastobart could become a valuable option for a subset of MSS mCRC patients who currently have limited therapeutic choices. Xilio’s next steps include further clinical validation, regulatory engagement, and securing a strategic partner to support the drug’s development and potential commercialization.
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