399P A Quality-adjusted Time Without Symptoms and Toxicity (Q-Twist) Analysis Comparing Nivolumab Plus Chemotherapy (N+CT) or Nivolumab Plus Ipilimumab (N+I) Vs CT in Patients (pts) with Tumor Cell PD-L1 ≥ 1% Advanced Esophageal Squamous Cell Carcinoma (ESCC): CheckMate 648