Cancer Vaccine Keeps Patient Disease-Free 6 Years
The most striking case involved a patient with metastatic colorectal cancer who was diagnosed in 2019 with advanced disease that had spread to the liver, lungs and lymph nodes. More than six years after receiving an experimental treatment, the patient remains without evidence of disease.
Treos Bio presented new clinical data at the EACR 2026 cancer research conference in Budapest, pointing to possible progress in the use of peptide-based immunotherapy against difficult-to-treat cancers.
The most striking case involved a patient with metastatic colorectal cancer who was diagnosed in 2019 with advanced disease that had spread to the liver, lungs and lymph nodes. More than six years after receiving an experimental treatment, the patient remains without evidence of disease.
The case is especially notable because the patient had MSS colorectal cancer, or microsatellite stable cancer, a form that usually does not respond well to immunotherapy. These tumors are often described as “cold,” meaning the immune system has difficulty recognizing and attacking them.
The patient received three doses of PolyPEPI1018, Treos Bio’s experimental vaccine, alongside maintenance chemotherapy. The vaccine is based on synthetic peptides designed to target seven cancer antigens. Following treatment, the tumors shrank enough to allow surgery.
After the operation, pathology tests found no living cancer cells in the liver, intestine or in 27 lymph nodes that were examined.
Laboratory testing showed that the vaccine triggered an immune response against all seven antigens included in the treatment. Active immune cells were found both in the patient’s blood and inside the tumor tissue, which may help explain the unusual response in a cancer type that is typically resistant to immune-based treatment.
Beyond the single colorectal cancer case, Treos Bio also presented a new platform called PEPI Panel, designed to make personalized cancer treatment faster and simpler. Unlike traditional approaches, the platform does not require a tumor biopsy. Instead, it can work from a blood or saliva sample.
The system uses a large database of synthetic peptides built from information taken from more than 100,000 tumors and around 16,000 HLA profiles. In an initial analysis of 11 patients with seven types of cancer, the platform predicted around 70% of the key antigens in each tumor. Among six patients who received personalized treatment based on the platform, 83% of the selected peptides triggered an immune response.
The company also presented a lung cancer case involving a patient with EGFR-mutated NSCLC whose disease had progressed despite earlier treatment. The patient received a personalized 11-peptide immunotherapy, also without a biopsy. Afterward, treatment with osimertinib led to a lasting reduction in lung and brain tumors for more than nine months.
Treos Bio said the findings support the potential of combining peptide-based immunotherapy with standard cancer treatments, especially in resistant cancers. The data is still early and based on a small number of patients, but it suggests a possible path toward making immunotherapy effective against tumors that have long been considered difficult for the immune system to reach.