VET3-TGI shows 71% response rate in cutaneous malignancies

By Amara Osei

At the September 2026 data cutoff, intratumoral VET3-TGI showed a 71% objective response rate in seven evaluable patients with cutaneous malignancies (skin cancers): one complete response (CR) and four partial responses (PRs). The phase 1/1b STEALTH-001 trial (NCT06444815) evaluated the agent in advanced solid tumors; investigators presented the data at the 2026 SITC Annual Meeting.

What did STEALTH-001 evaluate?

VET3-TGI is an oncolytic vaccinia virus encoding a TGF-β inhibitor and interleukin-12 (IL-12). Investigators administered the virus directly into tumors, either alone or with atezolizumab (Tecentriq), in patients with advanced solid tumors.

Twenty patients had received VET3-TGI by the cutoff: 16 as monotherapy and four with atezolizumab. For efficacy, investigators analyzed 12 patients with sufficient follow-up: seven with cutaneous malignancies and five with other non-cutaneous solid tumors.

The cutaneous group comprised three patients with Merkel cell carcinoma (MCC), three with melanoma, and one with cutaneous squamous cell carcinoma (cSCC). Investigators focused this subgroup after responses clustered in skin cancers.

Where did the responses occur?

Blinded independent central review found an objective response rate (ORR) of 42% and a disease control rate (DCR) of 75% across all 12 evaluable patients. In the seven-patient cutaneous subgroup, ORR reached 71%, comprising one CR and four PRs, compared with 42% overall.

All three patients with MCC responded, with one CR and two PRs. Two of three melanoma patients also responded. Responses occurred in non-injected lesions, although the report did not explain the mechanism or establish how frequently that pattern occurred.

The report did not divide the 12-patient efficacy set by monotherapy versus atezolizumab. The reported response data therefore cannot assign the observed activity to either administration strategy.

How durable were the responses?

All responders remained on study treatment at the data cutoff. Their treatment durations ranged from 10 to 19 months, while the median duration of response had not been reached. Treatment exposure is not identical to measured response duration, and the report supplied neither confidence intervals nor a numerical estimate for the median.

The cutaneous efficacy estimate derives from seven patients and three specific tumor types, while the program remained in expansion cohorts, with confirmatory studies still planned. The summary did not describe a randomized comparator or report overall survival. The response figures therefore provide a signal for further testing rather than a settled estimate of clinical benefit.

Why did investigators refocus on skin cancers?

Yana Najjar, MD, serves as associate professor of medicine and director of the Clinical and Translational Research Center at University of Pittsburgh Medical Center Hillman Cancer Center. Her account linked the response pattern to the program’s next development step.

Najjar said: “When we looked specifically at where those responses were occurring, they were occurring in patients with cutaneous malignancies, which is why we went on to really enrich and focus on that population.” Her explanation tied that enrichment to the program’s shift toward cutaneous malignancies.

The cutaneous cohort was heavily pretreated. Patients had received a median of three prior lines of therapy (range, one to nine), and every patient had progressed on anti–PD-1/PD-L1 immune-checkpoint therapy. More than 40% had also progressed after dual checkpoint blockade with a CTLA-4 inhibitor plus an anti–PD-(L)1 agent.

What did the safety data show?

Investigators reported no dose-limiting toxicities through the maximum feasible dose. Most treatment-related adverse effects were grade 1 or 2, indicating mostly mild or moderate events. The summary did not enumerate individual adverse events, their incidence, or achieved dose intensity, so tolerability cannot be judged from the response data alone.

What happens next?

Separate monotherapy and combination expansion cohorts focused on cutaneous malignancies remain ongoing. Additional studies are planned to confirm clinical activity in this population. For dermatology and oncology practices, VET3-TGI remains investigational in pretreated MCC, melanoma, and cSCC. The next test will come from the ongoing cutaneous expansion cohorts and additional studies seeking to confirm clinical activity.