Solstice Oncology
Solstice Oncology is a clinical-stage immuno-oncology company developing porustobart, a second-generation Fc-enhanced CTLA-4 antibody, in combination with anti-PD-1 therapy for the neoadjuvant treatment of early-stage cancers. The company's lead program targets microsatellite-stable (MSS) stage III colon cancer, a patient population historically unresponsive to immunotherapy. Porustobart's heavy-chain-only structure provides a shorter half-life (4-5 days) than first-generation CTLA-4 antibodies, potentially improving tolerability.
- Drug Discovery & Therapeutics
- Biotechnology
- Healthcare Technology
Funding
Raised to date
$225MRaised to date based on public sources. This may differ from the amount the company actually raised and is based only on what is publicly available on the internet.
across 1 round
$225M · Series A
Announced Sep 2026 · from article date
Disclosed cumulative: $225M
Founders
Founder details are not available yet.
Product
Problem
Most colon cancer cases are microsatellite-stable (MSS), a form that has historically not responded to immunotherapy, leaving patients with few options beyond surgery and chemotherapy. Approximately 30% of patients with stage III colon cancer are still not cured by surgery and chemotherapy today, and the disease is the second leading cause of cancer death in the United States.
Solution
Solstice Oncology is a clinical-stage immuno-oncology company developing porustobart, a second-generation, engineered CTLA-4 antibody, in combination with anti-PD-1 therapy for the neoadjuvant setting—before surgery—when the immune system is most intact. The two agents work synergistically: anti-PD-1 reawakens T cells that have already recognized the tumor, while porustobart releases a second, independent brake on the immune system and depletes immunosuppressive regulatory T cells that shield tumors from attack. This combination aims to generate a deeper and more durable anti-tumor response than either agent alone, and when given before surgery, primes a systemic immune response that reaches micrometastatic disease beyond the primary tumor. Porustobart's engineered, heavy-chain-only structure gives it a markedly shorter half-life than first-generation CTLA-4 antibodies, which may support a more favorable tolerability profile in early disease where patients are otherwise well.
Target Audience
Primary customers are clinical investigators, academic medical centers, and cancer centers conducting neoadjuvant immunotherapy trials, as well as patients with resectable MSS stage III colon cancer and other early-stage solid tumors who have had few immunotherapy options.
Features
- Lead program targets neoadjuvant MSS stage III colon cancer, with an additional undisclosed early-stage solid tumor program in Phase 1b
- Porustobart is a heavy-chain-only antibody with enhanced Fc-mediated Treg depletion in the tumor microenvironment, compared to first-generation CTLA-4 antibodies
- Shorter half-life than first-generation CTLA-4 antibodies (4-5 days vs. 15–18 days), potentially improving tolerability and enabling more flexible dosing
- Dual mechanism of action: checkpoint inhibition plus Fc-enhanced regulatory T-cell depletion via ADCC
- Clinical data cited show a 30% objective response rate with strong durability for porustobart + tislelizumab (PD-1) in late-line MSS CRC without liver metastases
- Programs designed toward curative endpoints, with a focus on early disease, systemic immune impact, and elimination rather than stabilization