Phio Pharma Concludes Enrollment in Phase 1b Trial of INTASYL siRNA PH-762

Phio Pharmaceuticals (PHIO) Completes Enrollment in Phase 1b Trial, Initial Data Shows Promise

Phio Pharmaceuticals (NASDAQ: PHIO), a clinical-stage biopharmaceutical company specializing in siRNA therapeutics, announced it has completed enrollment for its Phase 1b clinical trial of INTASYL siRNA candidate, PH-762. This trial focuses on the treatment of cutaneous squamous cell carcinoma (cSCC), melanoma, and Merkel cell carcinoma.

Key data revealed that of 18 patients enrolled across five dose-escalating cohorts, 16 were diagnosed with cSCC, yielding promising results: six patients achieved complete responses, two experienced near-complete responses, and two had partial responses. Moreover, a single patient with Merkel cell carcinoma exhibited a partial response. Importantly, the trial reported no dose-limiting toxicities or clinically significant treatment-emergent adverse effects.

The company is continuing treatment of additional patients in the fifth cohort with the highest dose, with pathology results anticipated in Q1 2026.

Positive

Enrollment completed for Phase 1b trial of PH-762

18 patients treated across five dose-escalating cohorts

6 complete pathologic responses in 16 cSCC patients

No dose-limiting toxicities or clinically relevant TEAEs reported

Pathology readouts for highest-dose cohort expected in Q1 2026

Negative

Seven patients showed pathologic non-response (

Single Merkel cell carcinoma patient achieved only a partial response

Efficacy data based on small cohort sizes (up to 18 patients)

Phase 1b enrollment complete; early pathology shows multiple complete responses and no dose‑limiting toxicities.
Phio completed enrollment in the Phase 1b trial of PH-762 and continues treating additional patients at the highest dose cohort; pathology readouts for those patients are expected in Q1 2026. The protocol delivers four weekly intratumoral injections and assesses pathologic response on day 36, with the trial covering cSCC, melanoma, and Merkel cell carcinoma (NCT# 06014086).

The disclosed outcomes in 18 treated patients include in 16 patients with cSCC: six complete responses (100% clearance), two near-complete responses (>90%), and two partial responses (>50%); one metastatic Merkel cell patient had a partial response (>50%). Six cSCC patients and one metastatic melanoma patient were non-responders ( clearance). The company reports no clinical progression, no dose-limiting toxicities, and no clinically relevant treatment-emergent adverse effects to date; it also reports that PH-762 was well tolerated across dose cohorts.

The immediate business mechanism is clinical proof-of-concept through intratumoral PD-1 silencing; the data show objective pathologic activity and a favorable tolerability signal in this small cohort. Key dependencies and risks remain: confirmatory pathology from the highest dose cohort expected in Q1 2026, the small sample size, and the trial’s early-phase design that limits generalizability. Watch the upcoming pathology readouts and the final safety dataset from the highest dose cohort over the next quarter; those items will materially affect how persuasive the early efficacy and safety signals appear within the trial’s stated endpoints.

November 25, 2025 – 11:30 AM

Phio Pharmaceuticals Corp. (PHIO), a clinical-stage siRNA biopharmaceutical company, announced the completion of enrollment in its Phase 1b clinical trial of INTASYL siRNA PH-762. The company is continuing to treat additional patients in the fifth cohort at the highest dose concentration of PH-762, with pathology results expected in Q1 2026.

PH-762 is designed to silence the PD-1 gene, a key target in various forms of skin cancer. The Phase 1b trial is evaluating the safety and tolerability of neoadjuvant use of intratumoral PH-762 in Stages 1, 2 and 4 cutaneous squamous cell carcinoma (cSCC), Stage 4 melanoma, and Stage 4 Merkel cell carcinoma. Patients receive four weekly injections of PH-762, and pathologic response is assessed on day 36 after the initial injection (NCT# 06014086).

To date, 18 patients with cutaneous carcinomas have completed treatment across five dose-escalating cohorts. Results from the trial include six complete responses (100% clearance), two near-complete responses (> 90% clearance), and two partial responses (> 50% clearance) in 16 patients with cSCC. A single patient with metastatic Merkel cell carcinoma had a partial response (> 50% clearance). Six patients with cSCC and one with metastatic melanoma had a pathologic non-response (50% clearance). No patients in the study exhibited clinical progression of disease.
The therapy was well tolerated with no dose-limiting toxicities or treatment-emergent adverse effects observed.

According to Robert Bitterman, CEO and Chairman of the Board of Phio Pharmaceuticals, completing enrollment in the Phase 1b trial “marks a significant step forward in advancing a promising treatment option for skin cancer.”

**The Science Behind INTASYL and PH-762**

Phio’s INTASYL platform leverages siRNA technology, a mechanism that inhibits gene expression. By silencing the PD-1 gene within tumor cells, PH-762 seeks to enhance the body’s immune response against the cancer. The intratumoral delivery aims to concentrate the therapeutic effect directly at the tumor site, minimizing systemic exposure and potential side effects.

**Market Implications and Competitive Landscape**

The market for skin cancer therapeutics is substantial and growing. The ongoing trial positions Phio Pharmaceuticals in a competitive landscape, targeting unmet needs in patients who may not benefit from existing treatments. Further clinical data releases, particularly the upcoming pathology readouts from the highest dose cohort expected in Q1 2026, will be crucial in determining its commercial potential and demonstrating if it can compete with existing anti-PD-1 therapies and other treatment modalities.

**Analyst Perspective**

Early results from the Phase 1b trial have sparked optimism, yet analysts caution that longer-term follow-up data and expanded trials will be necessary to establish the durability and broader applicability of PH-762. The company’s cash runway and funding strategy will also be critical factors to watch.

What did Phio announce about PH-762 enrollment on November 25, 2025?
Phio announced completion of enrollment in its Phase 1b trial of PH-762 with 18 patients treated across five cohorts.

What pathologic responses were reported for PH-762 in cSCC patients (PHIO)?
Among 16 cSCC patients, there were 6 complete responses, 2 near-complete90%), and 2 partial responses (>50%).

Were there safety concerns reported in the PH-762 Phase 1b trial (PHIO)?
No dose-limiting toxicities or clinically relevant treatment-emergent adverse effects were reported; PH-762 was described as well tolerated.

When will additional pathology results for PH-762 (PHIO) be available?
Pathology results for patients in the fifth, highest-dose cohort are expected in Q1 2026.

How many patients showed no pathologic response to PH-762 in the Phase 1b trial (PHIO)?
The release reports six cSCC patients and one metastatic melanoma patient with pathologic non-response (

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What Does This Mean For Investors?

The results of the trial were very promising, but it is important to keep in mind a few things. The sample size was limited, and the full pathology data for the highest dose is not available until 2026. Due to this available data, and the competitive skin cancer treatment market, proceed with caution. There is potential, but also uncertainty.

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