The estimated 3-year OS rate with botensilimab plus balstilimab was 48% in heavily pretreated recurrent ovarian cancer in the phase 1b C-800-01 trial.
Botensilimab in combination with balstilimab produced an estimated 3-year overall survival (OS) rate of 48% among patients with heavily pretreated recurrent ovarian cancer in the ovarian cohort of the phase 1b C-800-01 trial (NCT03860272), according to findings presented at the 2026 International Gynecologic Cancer Society Annual Global Meeting.¹
The estimated OS rate was unchanged from the 2-year estimate. Among the 35 patients evaluable for efficacy, the median OS was 14.8 months, and at the last follow-up, 25% of patients who had received at least 1 dose of treatment (n = 11/44) were alive and had stopped receiving all therapy.
“What stands out with longer follow-up is the survival plateau in patients who had already received multiple treatments,” Rebecca L. Porter, MD, of Dana-Farber Cancer Institute in Boston, Massachusetts, as well as a C-800-01 trial author, stated in a news release. “That pattern suggests that a different approach to activating the immune system may offer some patients lasting benefit, even when treatment options have narrowed.”
Botensilimab is an investigational multifunctional, Fc-enhanced, CTLA-4–directed antibody. Balstilimab is an investigational anti–PD-1 antibody.
The ovarian cohort enrolled patients with recurrent disease for whom no standard therapy was available or whose cancer had progressed after standard treatment. Patients had received a median of 4 prior lines of therapy, with 66% of patients having received at least 4 lines of therapy. All patients had previously received platinum chemotherapy, 77% of patients had received bevacizumab (Avastin), and 57% of patients had received a PARP inhibitor.
Botensilimab Plus Balstilimab in Recurrent Ovarian Cancer: C-800-01 3-Year Update
Approximately three-quarters of patients had platinum-resistant or refractory disease, defined as cancer that had progressed during platinum treatment or returned within 6 months of that therapy. The efficacy analysis included 35 patients who had undergone 1 or more tumor scans after starting therapy, and the safety population comprised all 44 patients who received treatment. The data cutoff was December 13, 2025.
Among the 35 efficacy-evaluable patients, the objective response rate (ORR) was 23% (n = 8), including 1 complete response (CR) and 7 partial responses (PRs), and the median duration of response was 9.7 months. Additionally, 31% of patients (n = 11) had a response or stable disease lasting at least 24 weeks. Responses and long-term survival were observed in both platinum-sensitive and platinum-resistant or refractory disease.
Among patients with platinum-resistant or refractory disease (n = 25), the estimated 3-year OS rate was 47%, with an ORR of 20% (n = 5), including 1 CR and 4 PRs. In patients with platinum-sensitive disease (n = 10), the estimated 3-year OS rate was 45%, with partial responses in 30% of patients (n = 3). Among patients who had received at least 4 prior lines of therapy (n = 23), the estimated 3-year OS rate was 48%, with an ORR of 17% (n = 4). In patients whose disease had progressed on a PARP inhibitor (n = 17), the estimated 3-year OS rate was 61%, with partial responses in 12% (n = 2). The safety findings remained consistent with the known safety profile of botensilimab plus balstilimab, with no new safety signals or treatment-related deaths reported.
In the broader phase 1b pan-tumor analysis of the C-800-01 trial, the estimated 2-year OS rate with botensilimab plus balstilimab was 39%, and in a separate cohort of patients with refractory microsatellite stable (MSS) metastatic colorectal cancer (mCRC) without active liver metastases, the estimated OS rates were 41% at 2 years and 33% at 3 years.
In previously reported phase 1 data from the CRC cohort of C-800-01, which enrolled patients with relapsed/refractory MSS mCRC, botensilimab plus balstilimab elicited an ORR of 17% (95% CI, 10%-26%) in response-evaluable patients (n = 101), with a disease control rate of 61% (95% CI, 51%-71%).² Responses were enriched in patients without active liver metastases (n = 77), who achieved an ORR of 22% (95% CI, 13%-33%) vs 0% (95% CI, 0%-14%) in those with active liver metastases (n = 24); the 1-year OS rate was likewise higher in patients without active liver metastases, at 69% (95% CI, 56%-79%) vs 30% (95% CI, 12%-49%) in those with active liver metastases.
