On December 23, 2025 Agenus Inc. (Nasdaq: AGEN), a leader in immuno-oncology innovation, reported the publication of clinical results from the ovarian cancer cohort of its Phase 1b C-800-01 trial evaluating botensilimab plus balstilimab (BOT+BAL) in The Journal for ImmunoTherapy of Cancer (JITC).

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The peer-reviewed manuscript titled, "Botensilimab (Fc-enhanced anti–CTLA-4 antibody) plus balstilimab (anti–PD-1 antibody) in patients with treatment-refractory ovarian cancer," is available online here.i

In this heavily pretreated population, BOT+BAL demonstrated clinically meaningful activity and durable benefit in women with treatment-refractory ovarian cancer, a population with few remaining options. The combination achieved a 23% overall response rate and 31% clinical benefit rate, including durable responses with a median duration of 9.7 months. Median overall survival reached 14.8 months, with an estimated of 75% of patients alive at 12 months.

These findings build on results from the broader C-800-01 dataset presented at ESMO (Free ESMO Whitepaper) 2025, where BOT+BAL showed activity across multiple refractory solid tumors. Collectively, these data reinforce the potential of BOT+BAL to generate meaningful immune responses in cancers historically considered unresponsive to immunotherapy.

High Unmet Need in Treatment-Refractory Ovarian Cancer

Ovarian cancer causes approximately 13,000 deaths annually in the U.S. and 200,000 globallyii,iii, and outcomes are particularly poor once tumors become platinum-resistant or platinum-refractory. Therapy with first-generation checkpoint inhibitors has yielded modest responses, with objective response rates between 8–10% and median progression-free survival of roughly 2 monthsiv,v, leaving many women with rapidly diminishing options and no approved immunotherapy combinations.

Publication Highlights

The study enrolled 44 women with treatment-refractory ovarian cancer who had received multiple prior lines of therapy. Nearly three-quarters were platinum-resistant or platinum-refractory, and most had high-grade serous tumors.
Activity was demonstrated in primary platinum-refractory patients—a rare and high-risk group often excluded from clinical studies.
Responses occurred in multiple ovarian cancer subtypes including high-grade serous, clear cell, and endometrioid tumors.
The BOT+BAL combination demonstrated a manageable and reversible safety profile, consistent with CTLA-4 and PD-1 therapy. Most common treatment-related adverse events such as diarrhea/colitis (43%; 16% grade 3), fatigue and nausea (36%) were effectively managed using established treatment guidelines. No treatment-related deaths were reported.
Steven O’Day, MD, Chief Medical Officer, Agenus, commented, "These results offer a meaningful signal of clinical activity for women with platinum-refractory ovarian cancer, a group that has seen little therapeutic progress. Botensilimab’s unique immune activation profile translated into clinically significant responses in a population long considered resistant to immunotherapy. These findings strengthen our confidence in BOT+BAL’s potential and support moving this combination into larger, randomized studies."

Rebecca Porter, M.D., Ph.D., Dana-Farber Cancer Institute and Lead Author added, "These women faced some of the most treatment-resistant forms of ovarian cancer, yet several achieved meaningful and durable benefit. Seeing this level of activity in such a heavily pretreated population is encouraging and provides important insights to the field regarding therapy approaches for patients with very limited remaining options."

Patient Access and Ongoing Development

BOT+BAL continues to advance through global clinical development across multiple tumor types. In parallel, eligible patients may be able to access BOT+BAL through regulatory-authorized early access mechanisms, including France’s AAC program, where treatment is reimbursed, as well as paid named-patient programs in select countries where permitted by local regulations. These programs are intended to provide access for patients with serious or life-threatening diseases who lack satisfactory therapeutic alternatives.

(Press release, Agenus, DEC 23, 2025, View Source;Balstilimab-in-Highly-Refractory-Ovarian-Cancer-Published-in-JITC/default.aspx [SID1234661612])