cDNA and Residual Disease After Chemoradiotherapy for Locally Advanced Head and Neck Squamous Cell Carcinomas

This study — called NeckTAR-IN — is investigating whether circulating tumor DNA (ctDNA) found in blood samples can detect residual cancer remaining after chemoradiotherapy in people with locally advanced head and neck squamous cell carcinoma. The goal is to help doctors identify who needs additional treatment after radiation and chemotherapy. **You may be eligible if...** - You are already enrolled in the parent NeckTAR study - You have signed written informed consent specifically for this sub-study (NeckTAR-IN) - You are covered by the French social security system **You may NOT be eligible if...** - You are not already a participant in the NeckTAR study - You have not provided written informed consent for this study - You are not covered by the French social security system Talk to your doctor to see if this trial is right for you.