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Long-Term Survival and Safety Data for BOT+BAL in Refractory MSS Metastatic Colorectal Cancer

Agenus

DOI: 10.26303/kaw0-h882

Key takeaways

  • In a heavily pretreated pan-tumor population, BOT+BAL produced a 17% confirmed objective response rate, a 66% disease control rate at six weeks, and a median response duration of 14.6 months. An estimated 39% of efficacy-evaluable patients were alive at 24 months.
  • In 123 patients with refractory MSS metastatic colorectal cancer without active liver metastases, median overall survival was 21.2 months, with 33% of patients alive at three years. Responses had a median duration of 16.6 months.
  • The breadth of activity across advanced solid tumors and the long-term MSS colorectal cancer findings support continued evaluation of BOT+BAL, including earlier in the course of MSS/pMMR colon cancer.

What is it about?

Across the clinical development program, botensilimab in combination with balstilimab in more than 1,500 patients across Phase 1 and Phase 2 trials. BOT+BAL has demonstrated clinical activity across more than nine tumor types, including in metastatic, late-line cancers and in earlier-stage disease treated in the neoadjuvant setting.

A substantial body of evidence in advanced disease comes from C-800-01 (NCT03860272), a large, multicohort Phase 1b study evaluating BOT+BAL in patients with advanced solid tumors refractory to standard treatment. Prior immunotherapy was permitted and the study included major cohorts of patients with MSS metastatic colorectal cancer, sarcoma, PD-1 relapsed or refractory non-small-cell lung cancer, ovarian cancer, and PD-(L)1 relapsed or refractory hepatocellular carcinoma, as well as patients with numerous other solid tumors.

  • The most recent pan-tumor analysis included 411 patients treated with BOT+BAL, of whom 339 had at least one post-baseline imaging assessment and were considered efficacy evaluable.
  • This was a heavily pretreated population: 61% of patients had received at least three prior lines of therapy, and 33% had previously received PD-(L)1 and/or CTLA-4 therapy.
  • Among efficacy-evaluable patients, the confirmed objective response rate was 17%, and the disease control rate at six weeks was 66%. Responses were durable, with a median duration of response of 14.6 months. Median overall survival was 17.2 months, and an estimated 39% of patients were alive at 24 months.
  • The study also generated long-term evidence in 123 patients with refractory MSS metastatic colorectal cancer without active liver metastases, a population in which conventional immunotherapy has historically shown limited activity. BOT+BAL produced a 20% objective response rate and a 69% disease control rate. Median duration of response was 16.6 months, median overall survival was 21.2 months, and the three-year overall survival rate was 33%.
  • Across the pan-tumor safety population, 32% of patients experienced a Grade 3 or higher treatment-related adverse event, and 22% experienced a Grade 3 or higher treatment-related immune-mediated adverse event. The most common immune-mediated adverse events involved the gastrointestinal system. No treatment-related deaths were reported.

Why is it important?

The C-800-01 findings provide clinical evidence that BOT+BAL can produce durable antitumor activity in patients with advanced cancers that have progressed after available treatments. Activity was observed across multiple tumor types and included patients previously treated with immunotherapy, supporting the potential for BOT+BAL to address mechanisms of immune resistance that can limit conventional immunotherapy.

The long-term MSS metastatic colorectal cancer findings are particularly important. MSS colorectal cancer is generally considered immunologically “cold,” and conventional PD-1 and CTLA-4 inhibitors have demonstrated limited activity in this setting. The depth and durability of response, together with the reported three-year survival, suggest that BOT+BAL can generate sustained immune control in a subset of patients despite advanced, heavily pretreated disease.

The pan-tumor and MSS colorectal cancer findings serve complementary roles. The broader analysis demonstrates activity across different refractory solid tumors, while the MSS colorectal cancer cohort provides mature, disease-specific evidence of durability and long-term survival.

The durability observed in advanced disease provides a strong clinical rationale for investigating BOT+BAL earlier in the course of MSS/pMMR colorectal cancer, when the immune system may have a greater opportunity to eliminate residual disease and prevent recurrence. Click on the next story below – 3. Evidence From NEST And UNICORN Supports the Potential of BOT+BAL in the Neoadjuvant Treatment Setting For MSS Colorectal Cancer – to examine the findings of the independent NEST and UNICORN studies of BOT+BAL before surgery.

Page published: 12-Nov-2026

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Who is involved?

Important information

In October 2026, BOT+BAL reached an important milestone with its first marketing authorizations in Armenia, where Botvymo® (botensilimab) and Evamplix® (balstilimab) were approved for use in combination in eligible adults with microsatellite-stable (MSS) metastatic colorectal cancer without active liver metastases who have previously received available standard therapies.

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