C-POST phase 3 trial of adjuvant (adj) cemiplimab (cemi) vs placebo (pbo) for high-risk cutaneous squamous cell carcinoma (CSCC): Updated overall survival (OS) and outcomes from circulating tumour DNA (ctDNA) analyses

C-POST

Patient / Population Intervention / Exposition Vergleich Endpunkt

In patients with high-risk cutaneous squamous cell carcinoma after surgery and postoperative radiotherapy, adjuvant cemiplimab improved disease-free survival compared with placebo.

N

415Patienten

Design

Phase 3, randomised 1:1, blinded, placebo-controlled trial of adjuvant cemiplimab (n=209) vs placebo (n=206) in patients with high-risk cutaneous squamous cell carcinoma (per nodal and/or non-nodal criteria) after surgery and postoperative radiotherapy (NCT03969004).

Endpunkt

Disease-free survival.

ErgebnisAt a median follow-up of 43.8 months, the disease-free survival HR was 0.46 (95% CI 0.31-0.67) with adjuvant cemiplimab vs placebo. Overall survival HR 0.63 (95% CI 0.36-1.11), with 51 deaths (cemiplimab 21 vs placebo 30). Median OS and DFS were not reached. Grade ≥3 treatment-emergent adverse events occurred in 25.4% vs 17.2%. Among patients with ctDNA data (cemiplimab 93, placebo 98), baseline MRD positivity was seen in 17 vs 19 patients. The DFS HR was 0.24 in MRD-positive and 0.45 in MRD-negative patients.

Rischin D, Porceddu SV, Day F, et al. Presented at ESMO Congress 2026, abstract LBA59, 25 October. Not yet published.

Diskussion & Kritik

With longer follow-up and the blind still in place, this update confirms a durable disease-free survival benefit for adjuvant cemiplimab in high-risk CSCC. The overall survival HR of 0.63 points the same way, but its 95% CI of 0.36-1.11 crosses 1 and it rests on only 51 deaths, so the abstract does not show a survival benefit and gives no P value or medians. The ctDNA analysis is exploratory and was run on a subset sampled after a protocol amendment. Its MRD-positive groups are small (17 vs 19) and the subgroup HRs are given without confidence intervals. Grade ≥3 adverse events were more frequent with cemiplimab, and the abstract does not say what they were.