On January 13, 2025 Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) reported positive results from the Phase 3 C-POST trial, which demonstrated that adjuvant treatment with PD-1 inhibitor Libtayo (cemiplimab) led to a statistically significant and clinically meaningful improvement in the primary endpoint of disease-free survival (DFS) in patients with high-risk cutaneous squamous cell carcinoma (CSCC) after surgery (Press release, Regeneron, JAN 13, 2025, View Source [SID1234649673]).

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"While surgery is curative for most people living with cutaneous squamous cell carcinoma, many are burdened with a higher risk of recurrence that can lead to death or disfiguration," said Danny Rischin, M.D., M.B.B.S., F.R.A.C.P., Research Lead, Head and Neck Cancer and Cutaneous SCC, Department of Medical Oncology at the Peter MacCallum Cancer Centre in Melbourne, Australia, and lead investigator of the trial. "At the first prespecified interim analysis, Libtayo achieved a remarkably high bar in improving disease-free survival in high-risk cutaneous squamous cell carcinoma. With no currently approved options in the adjuvant setting, these landmark results demonstrate Libtayo could represent a major advance in delaying recurrence in these vulnerable patients."

C-POST enrolled 415 patients with high-risk CSCC who were randomized to receive either Libtayo or placebo for up to 48 weeks. The primary endpoint was DFS, defined as time from randomization to the first documented disease recurrence or death due to any cause. At the first prespecified interim analysis for DFS with a median duration of follow-up of 24 months (range: 2-64 months), Libtayo demonstrated a 68% reduction in the risk of disease recurrence or death, compared to placebo (hazard ratio: 0.32; 95% confidence interval: 0.20-0.51; p<0.0001).

Safety was assessed in 205 patients in the Libtayo arm and 204 patients in the placebo arm. Adverse events (AEs) of any grade occurred in 91% and 89% of patients in the Libtayo arm and the placebo arm, respectively. Grade ≥3 AEs occurred in 24% and 14% of patients in the Libtayo arm and the placebo arm, respectively. Treatment discontinuations due to adverse reactions occurred in 10% and 1.5% of patients in the Libtayo arm and the placebo arm, respectively. Two patients experienced an AE leading to death in each arm.

Following these interim results, C-POST will continue for additional follow-up, including an analysis of the key secondary endpoint of overall survival. Detailed results will be presented at an upcoming medical meeting and will be shared with regulatory authorities with a plan for U.S. Food and Drug Administration (FDA) submission in the first half of 2025.

"Regeneron has long been a pioneer in non-melanoma skin cancer research. Libtayo was the first PD-1 inhibitor approved for certain patients with advanced cutaneous squamous cell carcinoma and has become a standard of care in this setting," said Israel Lowy, M.D., Ph.D., Clinical Development Unit Head, Oncology, at Regeneron. "With these results, Libtayo now has the potential to also transform the treatment of high-risk resectable cutaneous squamous cell carcinoma with adjuvant treatment. This trial is a testament to our unrelenting commitment to investigating areas where patient need remains high and to pursuing clinical research across diverse stages of skin cancer."

The potential use of Libtayo described above is investigational, and its safety and efficacy has not been evaluated by any regulatory authority for this indication.

About the Phase 3 Trial
C-POST is an ongoing randomized, placebo-controlled, double-blind, multicenter, global Phase 3 trial investigating Libtayo versus placebo as adjuvant treatment for patients with features associated with a high-risk of CSCC recurrence and who have completed surgery and post-operative radiation therapy. Trial participants are at high risk of recurrence due to nodal features (extracapsular extension or ≥3 involved lymph nodes) and/or non-nodal features (in-transit metastases, T4 lesion, perineural invasion, or locally recurrent tumor with ≥1 additional poor prognostic features).

For the first 12 weeks, Libtayo 350 mg or placebo is administered intravenously every three weeks, followed by Libtayo 700 mg or placebo administered intravenously every six weeks for 36 weeks. The primary endpoint is DFS, and the secondary endpoints include freedom from locoregional recurrence, freedom from distant recurrence, overall survival, cumulative incidence of second primary CSCC tumors, and safety.

The Trans-Tasman Radiation Oncology Group (TROG), with Dr. Rischin as lead investigator, collaborated with Regeneron on protocol development. Trial sites included 24 TROG sites in Australia.