TREOS Bio Reports Six-Year Cancer-Free Survival in MSS mCRC Patient Treated with PolyPEPI1018 Off-the-Shelf Immunotherapy
Key Insights
A patient with MSS metastatic colorectal cancer treated with PolyPEPI1018 in the OBERTO-101 trial remains disease-free over 77 months, with pathological complete response confirmed across resected tissues including liver lesions.
Translational analyses showed broad T-cell activation against all seven targeted antigens and treatment-induced T-cell clonotypes detected in both blood and tumor tissue.
TREOS Bio (search) also presented its PEPI Panel platform capable of predicting immunogenic peptide targets without tumor biopsy, achieving 83% T-cell response rates across six patients receiving PEPI-guided therapies.
TREOS Bio (search) has unveiled new clinical data at the European Association for Cancer Research (EACR) 2026 Congress demonstrating durable, long-term responses with its off-the-shelf peptide immunotherapy in microsatellite-stable metastatic colorectal cancer (search) (MSS mCRC) — a tumor type historically resistant to immunotherapy. The lead finding: a patient treated with PolyPEPI1018 at Mayo Clinic in 2019 remains cancer-free 77.2 months later, with pathological complete response (pCR) confirmed across all resected tissues.
The data, presented across three abstracts at the Budapest congress held June 8–11, reinforce the potential of TREOS Bio (search)'s proprietary Promiscuous EPItopes (PEPI) Technology to drive broad T-cell activation and durable clinical benefit in difficult-to-treat cancers.
Six-Year Disease-Free Survival in MSS mCRC
The OBERTO-101 trial (NCT03391232) case report, co-authored by Dr. Mojun Zhu of Mayo Clinic, Dr. Joleen Hubbard of Allina Health Cancer Institute, and the TREOS Bio (search) scientific team, details the clinical course of subject 01-0007. The patient presented with initially unresectable liver metastases, lesions in the colon and lung, and diffuse lymphadenopathy.
Following FOLFOX/cetuximab induction, the patient received three doses of PolyPEPI1018 alongside standard fluoropyrimidine-based maintenance therapy. Tumor shrinkage led to a partial response at week 36, enabling curative R0 surgery at week 56. Surgical pathology revealed no viable tumor cells across the liver, colon, and all 27 resected lymph nodes.
Translational analyses documented comprehensive immune activation: T-cell responses against all seven PolyPEPI1018-targeted antigens, increases in tumor-infiltrating lymphocytes (CD3+ and CD8+ cells) after the third dose, and PolyPEPI1018-specific T-cell clonotypes detected in both blood and tumor tissue. These findings support intratumoral expansion of treatment-induced immune responses targeting non-mutated shared antigens in MSS mCRC.
"These presentations highlight the potential of TREOS Bio (search)'s PEPI Technology (search) to support target prediction, broad T-cell activation and durable clinical benefit in difficult-to-treat cancers," said Sunjeet Sawhney, Chief Executive Officer of TREOS Bio. "They also reinforce the rationale for advancing PolyPEPI1018 in combination with standard therapies, while applying the PEPI Platform to additional immune-refractory cancers where current options remain limited."
MSS disease represents the vast majority of colorectal cancer patients and remains one of the largest unmet needs in cancer immunotherapy. PolyPEPI1018 has already been tested in three phase I/II clinical trials, and its off-the-shelf design could offer practical advantages over fully individualized approaches, including simpler logistics, faster treatment availability, and broader scalability.
Biopsy-Free Target Selection with the PEPI Panel
A third abstract introduces the PEPI Panel, a library of 3,286 synthetic long peptides covering 184 shared tumor antigens across 19 indications. Built using proprietary data from more than 100,000 tumors and 15,693 HLA genotypes, the Panel identifies peptide targets predicted to be immunogenic for individual patients using only a saliva or blood sample — eliminating the need for tumor biopsy.
Across 11 patients with seven tumor types, the PEPI Panel predicted approximately 70% of each patient's top tumor-expressed antigens. In six patients receiving PEPI-guided immunotherapies, 83% (60 of 72) of selected peptides induced T-cell responses. PEPI Panel-based treatments can be designed in days, supporting a potentially faster and less invasive approach to personalized cancer immunotherapy.
EGFR-Mutant NSCLC: Immunotherapy Followed by TKI Response
A second translational case report describes a 59-year-old patient with metastatic EGFR-mutant non-small cell lung cancer (search) (NSCLC) and brain metastases whose disease had progressed despite radiotherapy, EGFR-TKIs, chemotherapy, and chemo-immunotherapy.
Under the German "individueller Heilversuch" regulatory framework, the patient received an 11-peptide personalized immunotherapy designed without tumor biopsy, using HLA genotype and the PEPI Panel platform. De novo T-cell responses emerged against seven of 11 peptides, with no baseline responses detected. Subsequent tumor RNA-sequencing confirmed expression of eight of 11 predicted antigens. Following immunotherapy, subsequent osimertinib produced sustained regression of lung and brain lesions ongoing beyond nine months, accompanied by gene-expression signatures of an activated tumor microenvironment.
Leadership and Next Steps
The EACR presentations come shortly after TREOS Bio (search) announced the appointment of Sunjeet Sawhney as Chief Executive Officer. Sawhney brings more than 25 years of global oncology leadership experience, having previously served as CEO of Rappta Therapeutics and as Senior Vice President and Global Franchise Head of Oncology at Ipsen, with additional senior roles at Novartis and Roche.
TREOS Bio (search) is now preparing to advance PolyPEPI1018 through Phase 2B clinical development in MSS mCRC, a large patient population with significant unmet medical need.