Shares of Phio Pharmaceuticals Corp. (PHIO) advanced significantly in premarket trading on Wednesday, extending a sharp rally from the previous session. The biopharmaceutical company's stock climbed approximately 9.8% to $1.23 ahead of the opening bell, building on a substantial 24.4% gain recorded on Tuesday. This upward momentum is directly attributed to the release of updated clinical data from an ongoing early-stage trial for its lead oncology candidate.
Positive Safety and Efficacy Data from Phase 1b Study
The company provided a new analysis from its Phase 1b clinical trial evaluating PH-762 for the treatment of skin cancer. According to the update, the trial's Safety Monitoring Committee concluded its review and reported no serious adverse events or dose-limiting toxicities among the 22 participants who received four direct injections of the therapy into their tumors. The study employed a dose-escalation design, with the administered drug concentration increasing twentyfold from the lowest to the highest dose cohort.
Notably, the efficacy data was particularly encouraging at the highest dose level. Pathological assessment, which involves microscopic examination of removed tissue post-treatment, indicated that six out of seven patients exhibited a response. Furthermore, within a subgroup of 20 patients diagnosed with cutaneous squamous cell carcinoma, 13 demonstrated a pathological response, with nine of those achieving a complete response. The company also reported that no treated patients experienced disease progression during the study period.
Strategic Path Forward and Market Context
In response to these findings, Phio's management indicated plans to advance the highest dose concentration of PH-762 into subsequent clinical testing. The company is targeting a regulatory submission to the U.S. Food and Drug Administration (FDA) in the second quarter of 2026 to seek guidance on the next steps in the development pathway. Concurrently, key manufacturing milestones are on the horizon, with active pharmaceutical ingredient (API) material expected in March and current Good Manufacturing Practice (cGMP) production slated for the latter half of 2026.
PH-762 is an intratumoral therapy that utilizes small interfering RNA (siRNA) technology to locally silence genes involved in the PD-1 checkpoint pathway, a well-established target in cancer immunotherapy. This approach differs from the systemic anti-PD-1 antibodies marketed by major pharmaceutical firms like Merck (MRK) and Bristol Myers Squibb (BMY), offering a potentially differentiated mechanism of action.
The pronounced stock movement highlights the sensitivity of microcap biotechnology stocks like Phio to clinical data readouts. These companies often have limited trading liquidity and are highly susceptible to binary news events, which can cause significant volatility. While the initial safety and response data are viewed positively by the market, investors are cautioned that the results are from a limited early-stage trial. Full data are still subject to formal review, and the stock remains vulnerable to future developments, including potential trial delays, less robust follow-up data, or future capital raises that could dilute existing shareholders.
Market participants will now monitor whether the premarket enthusiasm sustains through the regular trading session or if profit-taking emerges following the recent surge. The focus for the company remains squarely on preparing its FDA submission for mid-2026 and executing on its stated manufacturing timeline.