Oncolytics Biotech (Nasdaq: ONCY) reported a median duration of response of 19.5 months for pelareorep in combination with bevacizumab and FOLFIRI in second-line KRAS-mutant, microsatellite-stable metastatic colorectal cancer, a figure the company describes as three to four times the historical benchmark of approximately four to six months in this setting. The data, if confirmed in a randomized study, would mark the first durable immunotherapy signal in a population where checkpoint inhibitors have no role.
The data come from the REO 022 study, a company-reported dataset in second-line RAS-mutant colorectal cancer patients. The trial is an early-phase study evaluating pelareorep added to the standard second-line backbone of FOLFIRI and bevacizumab in RAS-mutant, MSS metastatic colorectal cancer. Oncolytics has not disclosed the study phase, sample size, or primary endpoint in this release, which limits independent interpretation of the efficacy figures.
The objective response rate reported from REO 022 was 33% for patients receiving the pelareorep combination, compared to a standard-of-care benchmark of 6–11% drawn from published historical data. Oncolytics is framing the 19.5-month colorectal cancer response duration as the primary signal of interest, citing its potential relevance to accelerated approval endpoints. Cross-trial comparisons are limited by differences in patient selection, study design, and data maturity, and the historical benchmarks cited are not drawn from a concurrent control arm.
Oncolytics is currently enrolling patients in a randomized Phase II study designed as an open-label, multicenter trial in patients with RAS-mutated MSS mCRC who have received one prior oxaliplatin-based line of therapy. The company said it is actively engaging with the FDA to discuss a potential accelerated approval pathway based on response durability and time-to-event endpoints from this randomized study.
The population that Oncolytics is targeting sits at the intersection of two persistent problems in colorectal oncology. Microsatellite-stable disease accounts for roughly 85% of all metastatic colorectal cancer, and it is defined in part by its resistance to the checkpoint inhibitors that have transformed outcomes in MSI-H tumors. Within the MSS population, RAS mutations — spanning KRAS and NRAS across multiple codons — are present in the majority of patients and have historically been associated with poor prognosis and limited treatment options beyond cytotoxic chemotherapy and anti-angiogenic agents.
The approved second-line landscape for this population consists primarily of FOLFIRI combined with anti-angiogenic antibodies: bevacizumab, supported by the ML18147 data on continuation beyond progression; ziv-aflibercept, which received FDA approval in 2012 based on the VELOUR trial; and ramucirumab, approved in 2015 following the RAISE trial. These regimens produce median progression-free survival of approximately five to six months and median overall survival in the range of 12 to 13 months in the second-line setting. Response durability in the four-to-six-month range is consistent with what has been reported across these backbones.