Intervening early.
Designed to cure.

Solstice Oncology is a clinical stage immuno-oncology company developing a therapeutic that meets cancer at its most vulnerable moment, before surgery, to drive deep pathological response and return patients to lasting health. Our lead program is targeting colon cancer.

Intervene early.

MISSION

Achieve pathological response.

Return patients to lasting health.

A pie chart with sections in red and black on a black background.

Cancer's window of vulnerability is narrow.
We build immunotherapies calibrated to reach it — before disease advances, before resistance hardens, before options close.

Not management. Recovery.

Two clinical stage programs

PIPELINE

Our portfolio is built on porustobart in combination with anti–PD-1 therapy, advancing across early-stage cancers in the neoadjuvant setting — before surgery — where we believe the opportunity to improve cure rates is greatest.

View on ClinicalTrials.gov

Discovery Preclinical Phase 1 Phase 2 Phase 3

Program 1Porustobart + PD‑1

Neoadjuvant MSS stage III colon cancer · Lead Program

Program 2Porustobart + PD‑1

Neoadjuvant early-stage solid tumor · Undisclosed

1b

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OUR SCIENCE

Built around the narrowwindow
where disease
can be removed.

A brief window exists in which cancer can still be eliminated. Our programs are designed to reach it.

We don't wait until cancer has spread.

We intervene in the neoadjuvant setting — before surgery, when the immune system is most intact and the opportunity for a lasting cure is greatest.

We are developing porustobart, a second-generation, engineered CTLA-4 antibody designed to improve response rates, given in combination with anti–PD-1 therapy.

The two agents work synergistically. Anti–PD-1 reawakens T cells that have already recognized the tumor; porustobart widens that response by releasing a second, independent brake on the immune system and by depleting the immunosuppressive regulatory T cells that shield tumors from attack. Together they aim to generate a deeper and more durable anti-tumor response than either agent alone — and, given before surgery, an immune response that acts systemically, reaching micrometastatic disease well beyond the primary tumor.

Porustobart's engineered, heavy-chain-only structure also gives it a markedly shorter half-life than first-generation CTLA-4 antibodies, which we believe may support a more favorable tolerability profile in early disease, where patients are otherwise well.

How porustobart works.
And how it compares.

HOW IT WORKS

Two Mechanisms of Action

Mechanism of Action 1:

Checkpoint Inhibition

Mechanism of Action 2:

Fc-Enhanced Treg Depletion

Porustobart (originally discovered by Harbour BioMed) is investigational and has not been approved by any regulatory authority. Mechanism illustration is a simplified recreation.

HOW IT COMPARES

First Generation vs. Next Generation

FIRST-GENERATION
CTLA-4 BLOCKING ANTIBODIES

PORUSTOBART

Structure

Standard antibody structure: two identical heavy chains and two identical light chains

Heavy chain only antibody

Half-life

15–18 days

4–5 days

Treg depletionin tumor microenvironment

Not significant

Enhanced

Treatment settingfor clinical studies

Advanced/metastatic & early-stage solid tumors

Early-stage solid tumors Focus on neoadjuvant Tx

Response Ratewith anti-PD-1 in MSS mCRC*

<1%

30%

Grade ≥3 adverse eventsin MSS mCRC*

64%

46%

*In combination with anti-PD-1. References: Yervoy. Prescribing Information. BMS; 2011. Accessed August 5, 2026. Yervoy PI. Imjudo. Prescribing Information. AstraZeneca; 2022. Accessed August 5, 2026. Imjudo PI. Sharma A, et al. Anti-CTLA-4 Immunotherapy Does Not Deplete FOXP3+ Regulatory T Cells (Tregs) in Human Cancers. Clin Cancer Res. 2019 Feb 15;25(4):1233-1238. Gan Z, et al. An anti-CTLA-4 heavy chain-only antibody with enhanced Treg depletion shows excellent preclinical efficacy and safety profile. Proc Natl Acad Sci U S A. 2022 Aug 9;119(32):e2200879119. Clinicaltrials.gov. Chen EX, et al. Effect of Combined Immune Checkpoint Inhibition vs Best Supportive Care Alone in Patients With Advanced Colorectal Cancer: The Canadian Cancer Trials Group CO.26 Study. JAMA Oncol. 2020;6(6):831–838. Data on File.

Three convictions behind every program.

01
Early Disease

The greatest opportunity in oncology lies in treating disease earlier — when tumor burden is low, biology is less complex, and the body’s own immune system remains intact. Every program we run begins here.

02
Systemic Immune Impact

Immunotherapy does not act only on the tumor in front of us. Delivered before surgery, it primes an immune response that travels the whole body — reaching the micrometastatic disease that goes undetected and drives recurrence years later.

03
Eliminating disease

Our benchmark is elimination, not stabilization. Each program is designed toward a curative endpoint — therapies meant to end the disease, not just delay it.

Clinical Reason for Conviction

PD-1 and Fc-enhanced CTLA-4 elicits synergistic clinical response in metastatic MSS colon cancer

‍References: Le DT, et al. PD-1 Blockade in Tumors with Mismatch-Repair Deficiency. N Engl J Med. 2015 Jun 25;372(26):2509-20. Chen EX, et al. Effect of Combined Immune Checkpoint Inhibition vs Best Supportive Care Alone in Patients With Advanced Colorectal Cancer: The Canadian Cancer Trials Group CO.26 Study. JAMA Oncol. 2020;6(6):831–838. Schlechter B, et al. (2026, July 1-4). Botensilimab + Balstilimab in Microsatellite-Stable Metastatic Colorectal Cancer Without Active Liver Metastases: Extended Follow-Up and 3-Year Survival [Poster presentation]. ESMO-GI. Munich, Germany. https://www.esmo.org/meeting-calendar/esmo-gastrointestinal-cancers-congress-2026. Data on File.

Porustobart + tislelizumab (PD-1) showed strong durability in late-line MSS CRC without liver metastases

Spider Plot for tumor size (RECIST 1.1) from Harbour BioMed Study 4003.6 of CRC patients, evaluable set N=23; one patient had pseudoprogression and an adjusted BOR of PR

DEDICATION TO PATIENTS

Everything we do begins and ends with patients.

Colon Cancer

Colon cancer is one of the most commonly diagnosed cancers in the United States, and its incidence is rising sharply among younger adults. Most cases are microsatellite-stable (MSS) — a form that has historically not responded to immunotherapy. We are working to change that: intervening earlier, and bringing the potential of immunotherapy to patients who have had few options.

~109,000

Americans diagnosed with colon cancer each year

~1 in 5

new diagnoses now occur in people under 55*

2nd

leading cause of cancer death in the United States*

~30%

of patients with stage III colon cancer are still not cured by surgery and chemotherapy today

Sources: American Cancer Society
* Numbers for colorectal cancer; roughly two-thirds of which are colon tumors

Scientist in a lab examining a petri dish with a red liquid, wearing gloves and protective glasses.

COMMUNITY & RESOURCES

Clinical Trials

We are advancing a clinical program evaluating neoadjuvant porustobart in combination with anti–PD-1 therapy for people with early-stage cancers — beginning in resectable MSS stage III colon cancer, with additional early-stage programs to follow. Our studies are designed alongside leading academic investigators and cancer centers. If you are a patient, caregiver, or physician interested in learning more, we'd like to hear from you.

Full trial details and eligibility criteria are listed on ClinicalTrials.gov

GET IN TOUCH

ABOUT US

The people behind Solstice

Our team brings together many decades of combined drug development experience from companies and institutions such as Bristol Myers Squibb, Merck and Novartis — including multiple approved medicines and programs carried from first-in-human through registration.