A Phase III Randomized, Double-Blind, Placebo-controlled Study of Platinum(Cisplatin or Carboplatin) Plus Etoposide With or Without Toripalimab as First Line Therapy in Patients With ExtensiveStage Small Cell Lung Cancer

This is a phase III, multicenter, double-blinded, placebo-controlled study of platinum（Cisplatin or Carboplatin） plus etoposide with or without toripalimab as first Line therapy in patients with extensive stage small cell lung cancer. The purpose of this study is to evaluate the safety and efficacy of toriplimab in combination with platinum（Cisplatin or Carboplatin） plus etoposide in treatment naive extensive stage small cell lung cancer. Participants will receive asigned study treatment until progressive disease (PD) as assessed by the investigator using Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v1.1).