ESMO 2026 | C-POST: OS and exploratory ctDNA results of cemiplimab in CSCC

So the C-POST trial was a phase three adjuvant trial comparing simiplinab to placebo in patients with high-risk cutaneous SCC. We’ve previously reported a very significant difference in disease-free survival that has a ratio of 0.32 at the initial primary analysis. And based on those results, the drug has been approved, the FDA and the EMA. In this analysis, we’ve updated the disease-free survival data, but also the overall survival data and done some ctDNA analyses. The overall survival data was immature at the first analysis, and the hazard ratio was 0.86. On this updated analysis with a median follow-up of 43.8 months, the hazard ratio has reduced to 0.63, with 95% confidence limit still at the overlap one, with the upper limit of that being 1.11. Important to note that all patients, 90% of patients who recurred on the placebo arm were able to cross over to semiflumab. So despite that, we seem to be seeing a trend in improvement in overall survival. We also demonstrate that the disease-free survival benefit in an updated analysis is sustained with a hazard ratio of 0.46. There was a protocol amendment during this study that allowed patients to have their blood collected for ctDNA analyses. And we ended up with, out of the 415 enrolled patients, 286 were eligible for ctDNA blood collection, and we have a valuable data on 191 patients. Important to note that on this study, all patients had cross-sectional imaging before enrollment, so had no evidence of any gross local or distant disease at the time of this baseline ctDNA analysis. The other thing to note is that the assay that was used for the ctDNA analysis is a tumor-informed whole genome assay, which is ultra-sensitive and depends on, obviously on obviously individual patient tumor features. The proportion of patients that were MRD positive with CT DNA data was available was similar between the two arms at about 18 and 19% respectively, the patients had semiflumab or placebo. And what we saw with the ctDNA analysis was that irrespective of MRD status, there was benefit to semiflumab compared to placebo. The hazard ratio was 0.45 in the MRD negative and 0.24 in the MRD positive patients. What also was quite clear that in the placebo arm, patients who were MRD positive had a very poor outcome. So clearly MRD status was prognostic.