Cancer Vaccine Shows Promise, Leaving One Patient Disease-Free for More Than Six Years

Treos Bio presented new data at the EACR 2026 conference, showing that peptide-based immunotherapy was able to trigger a broad immune response even in “cold” tumors, alongside a new platform for developing personalized treatments without a biopsy.

At the European Association for Cancer Research conference, held in Budapest, the biotechnology company Treos Bio presented encouraging clinical data pointing to new potential in cancer immunotherapy, especially for tumors considered resistant to immune-based treatments. The focus of the presentation was a particularly unusual result: a patient with metastatic colon cancer, diagnosed in 2019 with advanced disease including metastases in the liver, lungs and lymphatic system, remained with no evidence of disease for more than six years after an experimental treatment.

This was an MSS (Microsatellite Stable) cancer, a type known to usually not respond to immunotherapy. The patient received three doses of the experimental vaccine PolyPEPI1018, based on synthetic peptides targeting seven cancer antigens. The treatment was given alongside maintenance chemotherapy and led to a significant shrinkage of the tumors, making surgery to remove them possible. Postoperative pathology tests found no live cancer cells, neither in the liver, nor in the colon, nor in 27 lymph nodes examined.

Laboratory analyses showed that the vaccine succeeded in stimulating an immune response against all seven antigens included in it, with active immune cells identified in both the blood and tumor tissue. These findings may help explain the unusual response in a “cold” tumor, one that is usually not well recognized by the immune system.

Beyond the individual case, the company also presented a new platform called PEPI Panel, intended to simplify and accelerate the development of personalized treatments. Unlike traditional approaches, the platform does not require a biopsy from the tumor, but relies only on a blood or saliva sample. The database includes thousands of synthetic peptides based on data from more than 100,000 tumors and about 16,000 HLA profiles. In an initial analysis of 11 patients with seven types of cancer, the system was able to predict about 70% of the key antigens in each tumor. Among six patients who received treatment tailored using the platform, 83% of the selected peptides succeeded in triggering an immune response.

The conference also featured another case from the field of lung cancer: a patient with NSCLC lung cancer carrying an EGFR mutation, whose disease progressed despite previous treatments, received personalized immunotherapy with 11 peptides, also without a biopsy. Afterward, treatment with the drug osimertinib led to a prolonged regression of tumors in the lungs and brain that lasted more than nine months.

The company says the findings reinforce the potential of combining peptide-based immunotherapy with standard treatments, especially in resistant cancers. Earlier this year, PolyPEPI1018 received IND approval from the FDA, and at the same time a collaboration was signed with GenDx to develop a companion diagnostic test based on HLA.

Although the data are still early and involve a small number of patients, the results presented point to an intriguing research direction, one that may expand the boundaries of immunotherapy to tumors that until now were considered “inaccessible” to the immune system.