Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2023

C-POST protocol update: A phase 3, randomised, double-blind study of adjuvant cemiplimab versus placebo post surgery and radiation therapy in patients with high-risk cutaneous squamous cell carcinoma (#233)

Danny Rischin 1 , Fiona Day 2 , Hayden Christie 3 , Gerry Adams 4 , James E Jackson 5 , Yungpo Su 6 , Vishal A Patel 7 , Joanna Walker 8 , Paolo Bossi 9 , Maite De Liz Vassen Schurmann 10 , Gaelle Quereux 11 , Amarnath Challapalli 12 , Suk-Young Yoo 13 , Shikha Bansal 13 , Israel Lowy 13 , Matthew G Fury 13 , Petra Rietschel 13 , Priscila Goncalves 13 , Sandro V Porceddu 14
  1. Department of Medical Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia
  2. Department of Medical Oncology, Calvary Mater Newcastle, , Waratah, Australia
  3. Cancer Care Centre Hervey Bay, Urraween, Australia
  4. Radiation Oncology, Genesis Cancer Care, Bundaberg, Australia
  5. Icon Cancer Centre Gold Coast, Southport, , Queensland, Australia
  6. Head and Neck Medical Oncology, Nebraska Cancer Specialists, Omaha, NE, USA
  7. Institute for Patient-Centered Initiatives and Health Equity, George Washington University School of Medicine & Health Science, Washington, DC, USA
  8. Department of Dermatology, The Perelman School of Medicine at the University of Pennsylvania, , Philadelphia , PA, USA
  9. Head and Neck Medical Oncology Unit, Humanitas University and Humanitas Cancer Centre, Milan, Italy
  10. Animi Oncology Treatment Unit, University Planalto Catarinense (UNIPLAC), Centro, Lages, Brazil
  11. Nantes Université, CHU Nantes, Department of Dermatology, Nantes, France
  12. Bristol Cancer Institute, University Hospitals Bristol & Weston NHS Foundation Trust, Bristol, UK
  13. Regeneron Pharmaceuticals, Inc., Tarrytown, NY, USA
  14. School of Medicine, University of Queensland, Herston, Queensland, Australia

Aims: Cure rates after surgery for cutaneous squamous cell carcinoma (CSCC) are >95%; however, radiation therapy (RT) is recommended postoperatively for patients at high risk of recurrence. Despite this, locoregional recurrence or distant metastases may still occur. The ongoing C-POST study (NCT03969004) is evaluating cemiplimab adjuvant therapy for patients with high-risk CSCC with recurrence after surgery and RT.

The key primary objective is to evaluate disease-free survival following treatment with adjuvant cemiplimab versus placebo in patients with high-risk CSCC who have tumour recurrence after surgery and RT. Secondary objectives include overall survival, freedom from locoregional or distant relapse, and treatment-emergent adverse events.

Methods: Patients with high-risk CSCC aged ≥18 years are eligible if they have undergone surgery and completed post-operative RT (minimum total bioequivalent dose 50 Gy) ≤10 weeks before randomisation and if the tumour presents with ≥1 of: (1) nodal disease with either extracapsular extension (ECE) and ≥1 node ≥20 mm, or ≥3 nodes denoted as positive for CSCC regardless of ECE; (2) in-transit metastases; (3) T4 lesion; (4) perineural invasion by clinical symptoms or radiological involvement; and (5) recurrent CSCC with ≥1 other risk factor.

The study has 2 parts. In part 1, patients will be randomised (1:1, blinded) to either intravenous cemiplimab 350 mg or placebo every 3 weeks for 12 weeks, followed by cemiplimab 700 mg or placebo every 6 weeks for 36 weeks. After 48 weeks of double-blind treatment, there is an optional part 2, where patients in either group who experience recurrence after a minimum of 3 months may receive open-label (unblinded) cemiplimab for up to 96 weeks.

Results: Ongoing enrolment is currently expected to reach 412 patients from approximately 100 sites across North and South America, Europe and the Asia-Pacific region.

Conclusions: The study is ongoing and actively recruiting.