Phase 1b/2 Study of LDRT in Combination With AK104 Plus Chemotherapy as First-line Treatment for ES-SCLC

Inclusion Criteria: * 18 to 80 years old. * Be able and willing to provide written informed consent and to comply with all requirements of study participation (including all study procedures). * Histologically or cytologically confirmed diagnosis of ES-SCLC per the Veterans Administration Lung Study Group (VALG) staging system. * No prior treatment for ES-SCLC. * Measurable disease, as defined by RECIST v1.1. * Eastern Cooperative Oncology Group performance status ≤ 1. * Life expectancy ≥ 3 months. * Adequate hematologic and end-organ function. * All female and male subjects of reproductive potential must agree to use an effective method of contraception, as determined by the Investigator, during and for 120 days after the last dose of study treatment. Exclusion Criteria: * Symptomatic or actively progressing Central nervous system metastases. * Uncontrolled carcinomatous meningitis. * Uncontrolled severe cancer pain * Uncontrolled pleural effusion, pericardial effusion or ascites requiring recurrent drainage procedures (once a month or more frequently). * Uncontrolled or symptomatic hypercalcemia. * History of autoimmune disease. * History of idiopathic pulmonary fibrosis, organizing pneumonia (such as bronchiolitis obliterans), drug-induced pneumonia, or idiopathic pneumonia, or evidence of active pneumonia on chest computed tomography (CT) during screening. * Active Tuberculosis infection. * Significant cardiovascular disease. * Major surgical procedure within 28 days p…