The 5-Fluorouracil Response and Optimization STudy (The FROST Trial): A Randomized Phase II Trial of Two Dosage Regimens (2D-Q2W vs 4D-Q3W) of 5-Fluorouracil (5-FU) in Patients With Platinum and PD-1 Inhibitor Pre-treated Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma | Arctuva