Adjuvant cemiplimab slashes recurrence risk in high-risk CSCC

Cemiplimab delivers a 68% reduction in recurrence risk after surgery and radiotherapy, setting a new potential standard in high-risk cutaneous squamous cell carcinoma (cSCC).

The monoclonal antibody and immune checkpoint inhibitor cemiplimab is already approved for the treatment of advanced cSCC. Now, Prof. Danny Rischin (Peter MacCallum Cancer Centre, Australia) presented the early results from the phase 3 C-POST trial (NCT03969004), which randomised 415 participants with resected high-risk cSCC 1:1 to cemiplimab or placebo for up to 48 weeks. Participants had high-risk features such as extracapsular nodal extension, multiple involved lymph nodes, T4 lesions, or perineural invasion. Most had head and neck primary tumours and were older males (median age 71) [1]. The results were simultaneously published in the New England Journal of Medicine [2].

With a median follow-up of 24 months, cemiplimab improved disease-free survival (DFS) by 68% compared with placebo (HR 0.32; 95% CI 0.20–0.51; P<0.0001). 2-year DFS rates were 87% versus 64% for cemiplimab and placebo, respectively. The benefit was consistent across all predefined subgroups. “This study clearly shows you can dramatically reduce the risk of recurrence,” Prof. Rischin explained. “These are very impressive differences.”

Cemiplimab also substantially reduced the risk of locoregional recurrence (HR 0.20; 95% CI 0.09–0.40; P<0.0001) and distant recurrence (HR 0.35; 95% CI 0.17–0.72; P<0.0001). No unexpected safety signals emerged: Grade ≥3 treatment-related adverse events occurred in 10% of participants on cemiplimab compared to <1% on placebo, primarily immune-related and consistent with PD-1 inhibition.

No overall survival benefit was seen at this early analysis stage. These findings support its potential role in the adjuvant setting, with ongoing trials exploring its use in the neoadjuvant space.

1. Rischin D, et al. Phase 3 trial of adjuvant cemiplimab (cemi) versus placebo (pbo) for high-risk cutaneous squamous cell carcinoma (CSCC). Abstract #6001, ASCO Annual Meeting 2025, 30 May–3 June, Chicago, IL, USA.
2. Rischin D, et al. N Engl J Med. 2025, 31 May; DOI: 10.1056/NEJMoa2502449.

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Posted on 30 July 2025