Shares of Phio Pharmaceuticals Corp (NASDAQ:PHIO) climbed 57.8% in premarket trading on Tuesday after the company released efficacy and safety data from its Phase 1b clinical trial for the INTASYL compound PH-762.
In the trial's final cohort, PH-762 produced an 85% pathological response rate, with 6 of 7 patients showing a treatment response. Among those six responders, four achieved a complete response characterized by 100% tumor clearance.
Across all five dose escalation cohorts, which included 22 enrolled patients who completed four intratumoral injections of PH-762, the company reported that no serious adverse events or dose-limiting toxicities were observed.
Commenting on the results, Robert Bitterman, President and CEO of Phio Pharmaceuticals, said, "These results support continued evaluation of this highest dose concentration of PH-762 in the next clinical trial."
Phio also reported an overall response rate of 65% among patients with cutaneous squamous cell carcinoma, or cSCC. Of the 20 cSCC patients, 13 were classified as pathologic responders, including 9 who achieved complete response, 2 with major or near-clear responses, and 2 with partial responses.
Looking ahead, the company intends to submit a proposal to the U.S. Food and Drug Administration seeking guidance on the design of subsequent clinical studies during the second quarter of 2026. Phio is simultaneously advancing its Chemistry, Manufacturing and Controls development; the company expects material to be available in March 2026 for a non-human primate study that is required before initiating pivotal human trials.
Context and implications
- Clinical efficacy: The high pathological and complete response rates in the final cohort support continued development of the highest dose concentration of PH-762.
- Safety profile: The absence of reported serious adverse events or dose-limiting toxicities across the enrolled cohorts is a favorable safety signal for further study.
- Regulatory and preclinical milestones: FDA guidance and completion of a non-human primate study are prerequisites cited by the company before pivotal trials can begin.