Tarrytown, New York, USA, October 25, 2026
Regeneron Pharmaceuticals has reported longer-term clinical data showing an increasing overall survival benefit with Libtayo® (cemiplimab) in patients with high-risk cutaneous squamous cell carcinoma (CSCC) following surgery and radiation therapy. Updated results from the Phase 3 C-POST trial, presented at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain, showed a 37% reduction in the risk of death among patients initially treated with Libtayo compared with placebo. The findings were based on a median follow-up of 44 months, extending earlier analyses and strengthening the evidence for adjuvant immunotherapy in this high-risk skin cancer population. The trial also showed sustained improvements in disease-free survival, including among patients whose blood tests did not detect minimal residual disease at baseline. These results reinforce the role of Libtayo in reducing the risk of cancer recurrence after definitive local treatment.
Phase 3 C-POST Trial Shows Increasing Survival Benefit
The global, randomized, double-blind, placebo-controlled C-POST Phase 3 trial evaluated Libtayo as adjuvant treatment in 415 patients with CSCC at high risk of recurrence after surgery and postoperative radiation therapy. Participants received Libtayo or placebo for up to 48 weeks. At a median follow-up of 44 months, the analysis showed a hazard ratio for overall survival of 0.63, corresponding to a 37% reduction in the relative risk of death compared with placebo. This represented an increase in the estimated benefit from a 14% risk reduction at 24 months and a 22% reduction at 30 months. The confidence interval for the latest overall survival estimate crossed 1.0, so the result should be interpreted as an emerging longer-term benefit rather than definitive proof of a statistically significant overall survival improvement. Importantly, 88% of placebo-treated patients who experienced recurrence subsequently received Libtayo, meaning the survival comparison remained favorable despite substantial crossover to active treatment. Disease-free survival benefits were sustained with longer follow-up, supporting the potential value of initiating treatment after surgery and radiation rather than waiting for the cancer to return.
Libtayo Demonstrates Benefit Across MRD Groups
The updated analysis also examined circulating tumor DNA (ctDNA) as a potential biomarker for minimal residual disease (MRD). MRD refers to small amounts of cancer that may remain in the body after treatment but are not detectable through conventional imaging or clinical examination. Researchers assessed baseline ctDNA data from 191 participants, including 93 patients in the Libtayo group and 98 in the placebo group. Libtayo improved disease-free survival in both MRD-negative and MRD-positive patients. Among patients who were MRD-negative at baseline, the hazard ratio for disease-free survival was 0.45, indicating a 55% reduction in the relative risk of a disease-free survival event compared with placebo. Among MRD-positive patients, the hazard ratio was 0.24, corresponding to a 76% reduction in relative risk. These findings suggest that the benefits of adjuvant Libtayo were not limited to patients with detectable ctDNA before treatment. However, this was an exploratory analysis, and ctDNA testing should not be used alone to determine treatment decisions without further clinical validation. The results support continued research into biomarkers that may help refine recurrence-risk assessment and identify patients who could benefit from adjuvant immunotherapy.
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PD-1 Immunotherapy Supports Post-Surgical Cancer Care
Libtayo is a fully human monoclonal antibody that targets the PD-1 immune checkpoint receptor on T cells. By blocking PD-1 signaling, the medicine helps restore immune-cell activity against cancer cells that use checkpoint pathways to evade immune surveillance. In high-risk CSCC, surgery and radiation can remove or control visible disease, but some patients remain vulnerable to recurrence because microscopic cancer cells may persist. Adjuvant immunotherapy aims to reduce this risk by supporting the body’s immune response after local treatment. The longer-term C-POST findings provide additional evidence for this approach in patients with high-risk disease. Safety findings remained consistent with previous analyses: treatment-emergent adverse events of any grade occurred in 94% of patients receiving Libtayo and 91% receiving placebo, while Grade 3 or higher events occurred in 26% and 17%, respectively. Treatment discontinuation due to adverse events was reported in 10% of the Libtayo group and 3% of the placebo group. Libtayo is approved in the United States and European Union for adjuvant treatment of eligible patients with high-risk CSCC following surgery and radiation. The updated findings strengthen the long-term clinical evidence supporting adjuvant Libtayo, while highlighting the importance of balancing potential benefits against treatment-related risks.
Source: Regeneron Pharmaceuticals press release
