Safety and feasibility of talimogene laherparepvec in peritoneal surface malignancies: Results from the TEMPO trial

Peritoneal surface malignancies (PSMs) remain a therapeutic challenge, particularly in patients with unresectable disease who cannot benefit from cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. The Talimogene Laherparepvec for the Treatment of Peritoneal Surface Malignancies (TEMPO) trial (NCT03663712) is the first phase 1, multicenter, open-label study to evaluate intraperitoneal (i.p.) administration of talimogene laherparepvec (T-VEC), an FDA-approved oncolytic virus, in this setting. Nineteen patients with unresectable PSMs from appendiceal, ovarian, small bowel, and peritoneal carcinomas were enrolled; 18 received treatment across three escalating dose cohorts (4 × 10⁶-4×10⁸ PFU). The primary endpoint was safety and tolerability, with secondary endpoints assessing viral kinetics and shedding, and an exploratory efficacy endpoint. T-VEC demonstrated a manageable safety profile, with gastrointestinal and systemic toxicities more frequent at higher doses but no dose-limiting toxicities; one case of grade 3 neutropenia was observed. Herpes simplex virus 1 (HSV-1) DNA exhibited a dose-dependent persistence pattern, peaking later in higher dose cohorts, while plasma and urine remained consistently negative, supporting biosafety. Clinically, one complete response and ten cases of stable disease (4-19 months) were observed, while six patients experienced progression. These findings establish the safety and feasibility of i.p. T-VEC for unresectable PSMs, demonstrate localized viral replication without systemic dissemination, and suggest preliminary signals of clinical activity warranting further investigation in larger, more diverse cohorts.