The High Stakes of REO 033: Can Pelareorep Scale Early Colorectal Cancer Wins?

In the world of oncology, early signals are often the siren song of biotech—promising, but notoriously difficult to replicate in controlled settings. For Oncolytics Biotech, as GlobeNewswire first reported, the focus is now squarely on the REO 033 trial, a study designed to determine if its lead candidate, pelareorep, can deliver a statistically significant win in patients with RAS-mutant, microsatellite-stable (MSS) metastatic colorectal cancer (mCRC).

According to reporting from GlobeNewswire, the REO 033 study is a randomized, controlled, open-label trial. It pits a combination of pelareorep, bevacizumab, and FOLFIRI (folinic acid, fluorouracil, and irinotecan) against the standard-of-care FOLFIRI and bevacizumab as a second-line treatment. The target population is specific: patients who have already progressed on first-line oxaliplatin-based therapy.

The impetus for this trial stems from an earlier study, REO 022. As reported by GlobeNewswire, that previous efficacy signal showed a progression-free survival (PFS) of 17 months, compared to 6 months for the historical standard of care. While that gap is substantial, the transition from an early signal to a registration-ready dataset is where many candidates falter. The REO 033 trial is the mechanism intended to validate those findings and generate the controlled data necessary for regulatory interactions.

From a design perspective, the trial is lean. GlobeNewswire notes that 30 patients per arm will be randomized. The primary endpoint is the objective response rate (ORR), while secondary endpoints include safety, tolerability, disease control rate, duration of response (DOR), overall survival (OS), and PFS.

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**Opinion:** In my view, the narrow patient population—specifically the MSS colorectal cancer cohort—makes this a high-risk, high-reward play. MSS tumors are famously resistant to many immunotherapies, meaning any consistent signal here would be a significant breakthrough. However, the small sample size of 60 total patients (30 per arm) means there is very little margin for error. If the REO 033 results mirror the 17-month PFS seen in REO 022, Oncolytics will have a powerful narrative. If the efficacy dips, the path to registration becomes significantly more complex.

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There is already a glimpse toward the finish line. GlobeNewswire reports that interactions with the U.S. Food and Drug Administration have opened the door for a pivotal expansion of the study, referred to as Part B. This expansion would build upon the current enrollment phase (Part A) and could potentially support an accelerated approval submission based on ORR, with full approval contingent on PFS data.