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BOT+BAL is an investigational combination of botensilimab (BOT), an anti-CTLA-4 antibody, and balstilimab (BAL), an anti-PD-1 antibody. Early results in a small, nonrandomized study of recurrent ovarian cancer showed responses in some patients, but the evidence does not establish the combination as standard treatment or show that it is better than other options.
What BOT+BAL is and how it is intended to work
Botensilimab and balstilimab are immune checkpoint antibodies being studied together. BAL blocks PD-1 from interacting with its ligands PD-L1 and PD-L2. BOT is an Fc-enhanced anti-CTLA-4 antibody, designed to engage activating Fc gamma receptors. The proposed rationale is that BOT may influence T-cell priming, regulatory T cells and myeloid cells, while BAL blocks a separate checkpoint pathway.
These mechanisms explain why researchers are testing the combination; they do not establish that a particular patient’s tumor will respond. BOT and BAL remain investigational medicines.
What the ovarian cancer study tested
The peer-reviewed ovarian-cancer report describes a cohort from C-800-01, an open-label, multicenter phase 1b study of botensilimab with or without balstilimab. The ovarian cohort enrolled people with confirmed recurrent disease for whom standard therapy was unavailable or had previously failed. Enrollment at nine U.S. sites ran from April 1, 2019, through November 8, 2023. The study included patients previously treated with checkpoint inhibitors.
#1 Best Overall
In the combination cohort, the study protocol used intravenous BOT at 1 or 2 mg/kg every six weeks and intravenous BAL at 3 mg/kg every two weeks, for up to two years. These are study-protocol details, not an approved dosing recommendation.
The primary report included 44 patients in its safety population, who had received a median of three prior lines of therapy. Efficacy was assessed in 35 patients. Median follow-up for that report was 9.6 months.
What results have been reported
In the 2025 peer-reviewed report, eight of the 35 efficacy-evaluable patients had a confirmed response: one complete response and seven partial responses. The study also reported clinical benefit, defined as a complete or partial response or stable disease lasting at least 24 weeks.
Rank #2
| Measure | Reported result |
|---|---|
| Confirmed objective response rate | 23% (8/35; 95% confidence interval [CI] 10%–40%) |
| Clinical benefit rate | 31% (11/35; 95% CI 17%–49%) |
| Median duration of response | 9.7 months (95% CI 2.8 months to not reached) |
| Median progression-free survival | 2.8 months (95% CI 1.4–5.5) |
| Median overall survival | 14.8 months (95% CI 12.1 months to not reached) |
| Overall survival at 12 months | 75% (95% CI 55%–86%) |
These figures come from a small, single-arm cohort, not a randomized comparison. The response rate describes how many patients had tumor shrinkage meeting the study’s criteria; it does not by itself show whether treatment extends life or works better than another therapy.
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Three-year follow-up reported in 2026
At the International Gynecologic Cancer Society (IGCS) meeting on October 3, 2026, Agenus reported an estimated overall survival of 48% at both two and three years among the same 35-patient efficacy group. Median overall survival remained 14.8 months. The company also reported that 11 of the 44 treated patients (25%) were alive and off treatment at last follow-up. The reported data cutoff was December 13, 2025.
This is a longer follow-up of the original cohort, reported by the company in a conference-data release, not an independent study or randomized trial. The estimate should not be interpreted as proof that BOT+BAL caused longer survival or is superior to another treatment.
Results by platinum sensitivity
The company’s 2026 report gave exploratory subgroup estimates. The overall cohort had received a median of four prior lines of therapy in this later report; all patients had previously received platinum, 77% had received bevacizumab and 57% a PARP inhibitor.
| Subgroup in Agenus’s 2026 report | Patients | Reported finding |
|---|---|---|
| Platinum-resistant or refractory | 25 | Estimated three-year overall survival 47%; objective response rate 20% (5/25) |
| Platinum-sensitive | 10 | Estimated three-year overall survival 45%; three patients had partial responses |
The subgroups are small, so these estimates cannot establish that benefit is equal across platinum-sensitivity groups. They are not a head-to-head comparison with other treatments.
Side effects and treatment discontinuation
In the 44-patient safety population in the peer-reviewed report, every patient experienced at least one treatment-emergent adverse event, and 89% had an event considered treatment-related. Diarrhea or colitis was the most common treatment-related adverse event, reported in 43% of patients; 16% had grade 3 diarrhea or colitis. Fatigue and nausea each occurred in 36%. Grade 3 or higher treatment-related adverse events occurred in 41%.
Nineteen patients (43%) stopped BOT and/or BAL because of a treatment-related adverse event. Immune-mediated enterocolitis and colitis were notable reasons. The report recorded no treatment-related deaths; Agenus’s 2026 update said there were no new safety signals or treatment-related deaths. For anyone considering a trial, the possibility of serious immune-related gut inflammation and treatment discontinuation is important to discuss with the oncology team.
Are there biomarkers that identify who might respond?
Exploratory analyses in the study associated response with higher levels of FcγRIIIA-positive/CD11c-positive cells and higher PD-L1 expression; tumors with T-cell infiltration were associated with clinical benefit. The report also described differences in immune architecture by histologic subtype. These observations are hypothesis-generating, not validated tests for choosing patients, and they do not provide a reliable way to predict an individual’s outcome.
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Agenus stated in its October 2026 release that BOT and BAL are in development and are not approved by the U.S. Food and Drug Administration. The company describes access before marketing authorization as limited to clinical trials and authorized early-access mechanisms where permitted by local rules. It says eligible patients treated in French hospitals under the AAC pathway and meeting predefined criteria may receive reimbursed treatment; availability and costs elsewhere vary by country.
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For current local options, patients should ask their oncology team about clinical-trial eligibility and consult the relevant trial or early-access authorities in their jurisdiction. Trial and access rules can differ by location.
How to put the evidence in context
The published ovarian-cancer evidence is an early-phase, uncontrolled cohort: 35 patients were efficacy-evaluable and 44 were included in the safety analysis. Without a randomized comparison, the results cannot establish comparative advantage over other treatments. The 2026 survival update adds follow-up to that same cohort; it does not increase the number of independent studies supporting the regimen.
When discussing BOT+BAL with an oncologist, useful questions include whether an appropriate trial is available, how its eligibility criteria relate to prior treatment and platinum sensitivity, what alternatives are appropriate for the person’s situation, and how immune-related toxicity would be monitored and managed.
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