Impact of Early Response to First-line Anti-PD-1 Monotherapy in Patients With Recurrent and/or Metastatic (R/M) Head and Neck Squamous Cell Carcinoma, Assessed by 18F-FDG PET/CT

This study is examining whether a special type of scan — called a PET/CT scan using a radioactive sugar — can predict early on which patients with advanced head and neck squamous cell carcinoma are responding to immunotherapy (anti-PD-1 treatment). If the scan can detect early response, doctors could potentially change treatment plans sooner for patients who are not responding. **You may be eligible if:** - You have been diagnosed with recurrent or metastatic head and neck squamous cell carcinoma (cancer of the mouth, throat, larynx, or related structures) - Your cancer is not suitable for surgery or radiation to cure it - Your tumor tests positive for PD-L1 (a protein that predicts immunotherapy response), with a Combined Positive Score (CPS) of 1 or higher - You are about to start or have just started first-line immunotherapy with an anti-PD-1 drug **You may NOT be eligible if:** - You have any medical condition that prevents you from safely receiving immune checkpoint inhibitor therapy Talk to your doctor to see if this trial is right for you.