Pembrolizumab and Trifluridine/Tipiracil With Previously Treated Advanced Gastric Cancer

arms : Pembrolizumab 400 mg every 6 weeks (Q6W), trifluridine/tipiracil at 35 or 30 mg/m2 twice daily (BID) for 5 days a week (D1-5, D8-12) with 2 days rest for 2 weeks, followed by a 14-day rest, repeated every 4 weeks (Q4W)