YL201 & AtezolizumabA Study of YL201 in Combination With Other Anti-Cancer Therapies in Patients With Advanced Solid Tumors

This is a phase Ib/II, multicenter, open-label study of YL201 combined with atezolizumab. The study will include 2 parts. Part 1 of the study is a dose escalation in participants with previously untreated ES-SCLC to determine the safety and tolerability of YL201 in combination with fixed dose of atezolizumab. The planned dose levels of YL201 are 1.2 mg/kg, 1.6 mg/kg and 2.0 mg/kg. Part 2 consists of a dose optimization stage followed by a dose expansion stage. During the dose optimization stage, participants will be randomized 1:1:1 to receive either YL201 at 1.2 mg/kg,1.6 mg/kg or 2.0 mg/kg Q3W in combination with fixed dose of atezolizumab. The decision to initiate the dose expansion stage in Part 2 and choose one or two of the YL201 dose level(s) will be based on the review of safety, PK, and efficacy from the dose optimization stage. Treatment will continue until disease progression, unacceptable toxicity, or withdraw of consent.