Adjuvant cemiplimab cut the risk of disease recurrence or death by 68% compared to placebo in the Phase 3 C-POST trial (HR 0.32; 95% CI 0.20–0.51; p<0.0001), and Regeneron brought late-breaking longer-term survival data from that same study to ESMO 2026 this week. The question those updated numbers answer is whether the disease-free survival benefit seen at the primary analysis holds as follow-up extends, since early landmark advantages in adjuvant immunotherapy trials sometimes compress over time.
The context matters because the FDA approved cemiplimab for adjuvant high-risk CSCC after surgery and radiation in October 2025, under Priority Review, meaning the C-POST primary data already formed the regulatory basis for approval. The ESMO readout therefore speaks to durability rather than regulatory destiny: clinicians and payers watching mature survival curves will use this data to judge whether the benefit seen at roughly two years is sustained well into the follow-up period. At the two-year mark in the primary analysis, the estimated disease-free survival rate favored cemiplimab substantially over placebo, setting a high bar for the longer-term update to clear.
Cutaneous squamous cell carcinoma is the second most common skin cancer, and high-risk cases after surgery and radiation have historically been managed without a proven systemic adjuvant option. Cemiplimab is the first immunotherapy approved in this adjuvant setting, which makes the C-POST maturation data commercially relevant: oncologists considering a one-year course of adjuvant PD-1 blockade will weigh whether longer follow-up narrows or preserves the hazard ratio seen in the primary cut. ESMO also served as the venue for Regeneron’s broader oncology portfolio, with data across multiple tumor types and cancer-associated complications presented across the meeting.
The number to watch in the late-breaking C-POST update is whether the hazard ratio holds near 0.32 or drifts toward 1.0 as censoring increases, since any meaningful convergence of the survival curves would sharpen the debate over treatment duration and patient selection in high-risk CSCC.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
