On May 31, 2025 Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) reported detailed analyses from the Phase 3 C-POST trial, which evaluated PD-1 inhibitor Libtayo (cemiplimab) in patients with high-risk cutaneous squamous cell carcinoma (CSCC) after surgery (Press release, Regeneron, MAY 31, 2025, View Source [SID1234653550]). The results, shared during an oral session at the 2025 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting and simultaneously published in the New England Journal of Medicine (NEJM), include additional data for the primary endpoint of disease-free survival (DFS) and the first presentation of key secondary endpoint outcomes.

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"While surgery and radiotherapy remain the cornerstones of treatment for high-risk cutaneous squamous cell carcinoma, there is a critical unmet need for systemic therapies to help prevent relapse and metastasis to ultimately drive better outcomes for patients," 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. "The Phase 3 C-POST trial demonstrates that cemiplimab is a highly active therapy in high-risk CSCC, with clinically meaningful outcomes across primary and secondary endpoints and exceptionally low rates of locoregional and distant recurrence."

Results from the C-POST trial shared earlier this year established Libtayo as the first immunotherapy to show a statistically significant and clinically meaningful benefit in high-risk CSCC in the adjuvant setting. In contrast, negative results with another PD-1 are presented at ASCO (Free ASCO Whitepaper). The data with Libtayo at this year’s ASCO (Free ASCO Whitepaper) provide additional insights for the primary endpoint of DFS – defined as time from randomization to the first documented disease recurrence or death – as well as first results for the secondary endpoints of freedom from locoregional recurrence, freedom from distant recurrence and overall survival (OS).

With a median duration of follow-up of 24 months (range: 2-64 months), efficacy results for Libtayo compared to placebo, were as follows:

68% reduction in the risk of disease recurrence or death (hazard ratio [HR]: 0.32; 95% confidence interval [CI]: 0.20-0.51; p<0.0001), with median DFS not reached for Libtayo-treated patients (versus 49 months for placebo)
At two years, DFS was 87% with Libtayo versus 64% with placebo
80% reduction in the risk of locoregional recurrence (HR: 0.20; 95% CI: 0.09-0.40)
65% reduction in the risk of distant recurrence (HR: 0.35; 95% CI: 0.17-0.72)
Updated OS data from a recent data cut, with approximately six months of additional follow up after the primary analysis for DFS, suggest an emerging OS benefit for Libtayo (HR: 0.78; 95% CI: 0.39-1.56) versus placebo.

"These results show the continued promise of Libtayo in non-melanoma skin cancers," said Israel Lowy, M.D., Ph.D., Clinical Development Unit Head, Oncology, at Regeneron. "Libtayo is the first medicine to demonstrate a statistically significant benefit in patients who have high-risk features for recurrence after resection of cutaneous squamous cell carcinoma and has the potential to become a new standard of care in the adjuvant setting. We are working with global regulatory authorities to bring this new option to patients as quickly as possible."

Additionally, an exploratory analysis of the C-POST results showed similar rates of DFS regardless of PD-L1 expression level. Specifically, Libtayo reduced the risk of disease recurrence or death by 72% in tumors with PD-L1 ≥1% (HR: 0.28; 95% CI: 0.15-0.52; n=309) and by 68% in tumors with PD-L1 <1% (HR: 0.32; 95% CI: 0.12-0.86; n=85), compared to placebo.

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. The most common AEs occurring in at least 10% of patients in the Libtayo arm were fatigue, pruritus, rash, diarrhea, arthralgia, hypothyroidism and maculo-paplar rash. The only grade ≥3 AE that occurred in more than 2% of patients in the Libtayo arm was hypertension. Treatment discontinuations due to AEs, regardless of attribution, occurred in 10% and 2% of patients in the Libtayo arm and the placebo arm, respectively. Two patients experienced an AE leading to death in each arm.

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.

Regulatory applications have been submitted for Libtayo in the treatment of adjuvant CSCC in the United States and European Union.

About the Phase 3 Trial
C-POST is one of several trials from Regeneron’s oncology portfolio and pipeline being shared at ASCO (Free ASCO Whitepaper).

C-POST was a 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 had completed surgery and post-operative radiation therapy. Trial participants were 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).

The trial enrolled 415 patients who were randomized to receive either Libtayo (n=209) or placebo (n=206) for up to 48 weeks. For the first 12 weeks, Libtayo 350 mg or placebo was administered intravenously every three weeks, followed by Libtayo 700 mg or placebo administered intravenously every six weeks for 36 weeks.