Replimune Group announces CERPASS trial of CSCC did not meet primary endpoints

Replimune Group announced results from the primary analysis of the CERPASS trial evaluating RP1 in combination with cemiplimab for the treatment of locally advanced or metastatic cutaneous squamous cell carcinoma and provided initial data for all patients in the anti-PD1 failed melanoma cohort of the IGNYTE clinical trial. Results from the CERPASS Trial in CSCC: The study did not meet either of the two primary endpoints of complete response rate or overall response rate as assessed by blinded independent central review. RP1 in combination with cemiplimab increased the CRR versus cemiplimab alone, which was just short of the required threshold for statistical significance in this study. Notably, among the 83 patients with locally advanced disease, the complete response rate in the RP1 plus cemiplimab group was 48.1% versus 22.6% in the cemiplimab only group. The ORR was comparable between the two study groups. Importantly, RP1 in combination with cemiplimab also increased duration of response as compared to cemiplimab alone, however, these data are immature and further follow up is required. Of note, RP1 plus cemiplimab provided particularly meaningful clinical activity for many patients with difficult to treat, disfiguring tumors that typically have the greatest impact on quality of life, given their size and location. There was also an imbalance in baseline tumor burden across the treatment groups which may have impacted the number of responses seen. A significantly greater number of patients with high baseline tumor burden were treated in the RP1 plus cemiplimab group as compared to the cemiplimab alone group. The trial will continue as planned to assess DOR, progression free survival and overall survival with greater maturity. Initial Data from All Patients in the IGNYTE Cohort of RP1 in Anti-PD1 Failed Melanoma: The registration directed anti-PD1 failed melanoma cohort from the IGNYTE clinical trial includes 140 patients and completed enrollment earlier this year. In the RP1 plus nivolumab group, the ORR was 31.4% with a CR rate of 12% showing activity consistent with the prior snapshot of 91 anti-PD1 failed melanoma patients. In the full population, almost half of patients failed combination therapy with ipilimumab plus nivolumab as compared to the earlier snapshot where approximately a third were ipilimumab and nivolumab failures. Approximately 50% of patients experienced clinical benefit, defined as CR, PR, or stable disease. Of responders, 100% are ongoing at more than six months with 78% of responses still ongoing as of November 6, 2023. Responses reported for this snapshot were investigator-assessed. RP1 combined with nivolumab continues to be well-tolerated, with mainly Grade 1-2 “on target” side effects, observed.