Cemiplimab (Libtayo) Receives FDA Approval for Adjuvant Treatment of Cutaneous Squamous Cell Carcinoma
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On October 8, 2025, the FDA approved, for adults with cutaneous squamous cell carcinoma at high risk of recurrence after surgery and radiotherapy, cemiplimab (Libtayo, Regeneron Pharmaceuticals Inc.) , an immunotherapy, as adjuvant treatment . This article examines why the approval matters, the studies supporting it, and cemiplimab's history in detail.
A New Adjuvant Treatment Option in Skin Cancer
Cutaneous squamous cell carcinoma (CSCC) is a skin cancer associated with sun exposure and common in older people. Although often detected and treated early, it carries a high recurrence risk in some patients and may return despite treatment.
There is therefore a need for adjuvant (additional) treatmentto prevent recurrence after surgery and radiotherapy. This new FDA approval for cemiplimab could fill that critical gap. It is groundbreaking both for CSCC patients and for expanding immunotherapy use in the adjuvant setting.
What Is Cemiplimab? How Does It Work?
Cemiplimab-rwlc, marketed as Libtayo, is a PD-1 inhibitordeveloped by Regeneron Pharmaceuticals and Sanofi. By targeting PD-1, which prevents the immune system from fighting cancer cells, it enables T-cell activation against tumors.
Like other drugs in its class, such as pembrolizumab and nivolumab, cemiplimab releases the immune system's brakes. It showed effective results early, particularly in cutaneous squamous cell carcinoma. The FDA therefore granted accelerated approval for advanced CSCC in 2018. Its efficacy has now also been established in the adjuvant setting.
📊 The C-POST Study: A 3-Fold Reduction in Recurrence Risk With Cemiplimab
Approval for adjuvant cemiplimab is based on a trial involving 415 patients, C-POST a randomized, double-blind, placebo-controlled clinical trial. All patients had surgery followed by adjuvant radiotherapy and were classified as high-risk for recurrence. They were randomized within 2 to 10 weeks after adjuvant radiotherapy.
🧾 Which Patients Are at "High Risk of Recurrence"?
Adjuvant approval for cemiplimab is based on the C-POST trial and its definition of high-risk cutaneous squamous cell carcinoma. Patients in this group had at least one of the following characteristics:
- Lymph node involvement: At least one pathologically positive lymph node
- Extranodal extension (ENE): Disease extending outside the lymph node
- Tumor size ≥ 4 cm
- Deep invasion: Muscle, bone, or subcutaneous tissue involvement
- Positive surgical margin (R1): Residual disease that cannot be re-excised
- Perineural invasion (PNI): Involvement of a nerve ≥0.1 mm in diameter
- Severe immunosuppression: (Excluding organ transplantation)
- T3–T4 disease at initial diagnosis (AJCC 8)
Adjuvant cemiplimab should be considered after surgery + radiotherapy in patients with:
- Lymph node involvement
- PNI (+), ENE (+), an R1 margin, or a tumor ≥4 cm
- Muscle–bone invasion or T3–T4 tumors
The following groups were not included in C-POST and should not be recommended cemiplimab:
- Organ transplant recipients
- People receiving immunosuppressive treatment for autoimmune disease within the past 5 years
- Those with uncontrolled HIV or active hepatitis B/C infection
- Those without RT or with low-risk T1-T2 tumors
Patients were randomized 1:1 to cemiplimab or placebo . The primary endpoint was the time to recurrence or death from any cause, defined as disease-free survival (DFS) .
- Cemiplimab arm: Median DFS not yet reached (CI: not calculable)
- Placebo arm: Median DFS 49.4 months (CI: 48.5 – NE)
- Risk reduction: 68% (HR: 0.32; CI: 0.20 – 0.51)
- Statistical significance: p < 0.0001
These impressive results show that cemiplimab dramatically reduces recurrence risk and may potentially improve long-term survival.
💉 Dosing Schedule and Safety Warnings
The recommended adjuvant cemiplimab schedule is:
- First 12 weeks: 350 mg IV every 3 weeks
- Thereafter: 700 mg IV every 6 weeks or 350 mg IV every 3 weeks
- Total duration: Until recurrence, unacceptable toxicity, or a maximum of 48 weeks
- Immune-mediated adverse effects, such as pneumonitis, hepatitis, and colitis
- Infusion-related reactions
- Complications after allogeneic stem cell transplantation
- Embryo-fetal toxicity risk (must not be used during pregnancy)
🕰 Cemiplimab's FDA and EMA Approval Journey
- October 8, 2025: Adjuvant approval for high-risk cutaneous squamous cell carcinoma (FDA)
- February 22, 2021: First-line approval in non-small-cell lung cancer with PD-L1 ≥50%
- February 9, 2021: First immunotherapy approval for advanced basal cell carcinoma
- September 28, 2018: First FDA approval for advanced cutaneous squamous cell carcinoma
Cemiplimab is an important immunotherapy that has shown potential in multiple cancers throughout development and progressed through rapid approval processes.
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