TREOS Bio Announces Publication of Phase 1b Clinical Trial Results of PolyPEPI1018 Plus TAS-102 in Refractory MSS mCRC in JCO Oncology Advances

First study to report promising activity for an active immunotherapy combined with TAS-102 (LONSURF®) in late-stage MSS mCRC; TREOS advances Phase II programme with Charité – Universitätsmedizin Berlin and Junshi Biosciences

LONDON, Nov. 06, 2025 (GLOBE NEWSWIRE) -- TREOS Bio today announced the publication in Journal of Clinical Oncology - Oncology Advances of results from OBERTO-201 (NCT05130060), a Phase 1b study evaluating PolyPEPI1018, an off-the-shelf multi-peptide immunotherapy, in combination with oral chemotherapy TAS-102 (LONSURF®) for patients with refractory microsatellite-stable metastatic colorectal cancer (MSS mCRC)—a population with minimal response to current immunotherapies. The study was conducted by Mayo Clinic and supported by a U.S. Government grant.

In this single-arm trial (n=15) after two prior metastatic treatment lines, PolyPEPI1018 + TAS-102 was generally well tolerated. PolyPEPI1018-related adverse events were limited to Grade 1–2 local injection-site reactions with no immune-related systemic toxicities observed. The combination achieved a 53.3% disease control rate (DCR); median progression-free survival (mPFS) was 4.0 months and median overall survival (mOS) was 8.7 months, representing promising improvements versus historical TAS-102 monotherapy. Patients with longer PFS and OS mounted broader cellular and humoral responses to PolyPEPI1018-targeted antigens. Exploratory analyses indicated more favourable outcomes in patients without active liver metastases at baseline; moreover, patients predicted based on HLA genotype to mount broader PolyPEPI1018-specific T-cell responses had longer survival (mOS 10.3 vs 4.6 months; HR=0.28).

“These results show that PolyPEPI1018 can generate broad anti-tumour immune responses in one of the most immunotherapy-resistant solid tumours,” said Dr Joleen Hubbard, principal investigator of OBERTO-201 and lead author. Dr Hagop Youssoufian, Chair of Medical Strategy of TREOS Bio and Adjunct Professor of Medicine at Brown University, added: “They reinforce our precision-immunotherapy strategy and support prospective patient selection using our computational HLA biomarker.”

Next steps and programme context

OBERTO-201 was initiated before the SUNLIGHT trial established TAS-102 plus bevacizumab as a new standard of care. Critical data from OBERTO-201, together with results from TREOS’ OBERTO-301 trial (PolyPEPI1018 plus atezolizumab in refractory MSS mCRC; ASCO 2024, Abstract 3594), informed the design of TREOS’ Phase II clinical programme in late-stage MSS mCRC, to be conducted in collaboration with Charité – Universitätsmedizin Berlin and Junshi Biosciences.

About Microsatellite-Stable Colorectal Cancer

MSS CRC represents ~85% of all colorectal cancer cases and affects an estimated 130,000 new patients annually in the United States and over 1.6 million globally. Current immunotherapies, including checkpoint inhibitors, have shown limited efficacy in this population.

About TREOS Bio

TREOS Bio, headquartered in London, is a clinical-stage company introducing a computational, biomarker-guided approach to cancer immunotherapy to address patient and tumour heterogeneity. We use proprietary therapeutic peptides, manufactured via commercially scalable processes without the need for tumour biopsy, to stimulate cancer-specific immune responses in patients predicted by our diagnostic tests to respond. TREOS is advancing clinical development of PolyPEPI1018 immunotherapy for metastatic colorectal cancer and progressing preclinical programmes for additional solid tumours. Our patient-focused design also enables rapidly formulated personalised immunotherapies. TREOS Bio has partnerships with leading institutions including Mayo Clinic, Charité – Universitätsmedizin Berlin, Roche, and Junshi Biosciences.

For more information, visit www.treosbio.com

Forward-Looking Statements

This press release contains forward-looking statements regarding TREOS Bio’s clinical development plans and anticipated timelines. Actual results may differ materially from those indicated by such forward-looking statements.

Media/IR Contact:
IR@treosbio.com

References (selection):

1. JCO Oncology Advances: OBERTO-201 Phase 1b results
   https://ascopubs.org/doi/10.1200/OA-25-00108
2. ASCO 2024, Abstract 3594: OBERTO-301 Phase 2 results 
   https://www.treosbio.com/publications