To Evaluate the Efficacy of Durvalumab + Anlotinib in Terms of OS and PFS.

This is an open-label, randomised, multicenter, Phase II study. This study is planned to enroll 90 eligible patients to receive durvalumab combined with up to 4 cycles of etoposide and platinum-based chemotherapy (EP). And approximately 64 patients who complete the 4 cycles of durvalumab + EP treatment and don't have progressive diseases (Non-PD patients) will be randomized in a 1:1 ratio to receive maintenance treatment durvalumab + anlotinib (Arm 1) or durvalumab (Arm 2) until confirmed progressive disease. Prophylactic cranial irradiation (PCI) is allowed at the investigators' discretion as per SoC guidance for ES-SCLC. Patients will attend a safety follow up visit 90 days after last dose of durvalumab. Tumor assessments will be performed at Screening with follow-up at Week 6 ±1 week and Week 12 ±1 week from the date of the first cycle treatment, and then every 8 weeks ±1 week until confirmed objective disease progression.

Target subject population Adult patients (aged ≥18 years) with histologically or cytologically documented extensive disease (American Joint Committee on Cancer Stage (8th edition) IV SCLC \[T any, N any, M1 a/b\]), or T3-4 due to multiple lung nodules that are too extensive or have tumor/nodal volume that is too large to be encompassed in a tolerable radiation plan. Patients must have World Health Organization/Eastern Cooperative Oncology Group performance status of 0-1, weight \> 30 kg and adequate organ and marrow function. All patients are suitable for firstline platinum-based chemotherapy. Duration of treatment Unless specific treatment discontinuation criteria are met, patients in Arms 1 and 2 will continue therapy until disease progression, as per investigator assessment. Investigational product, dosage and mode of administration Durvalumab 1500 mg will be administered for all patients via IV infusion concurrently with EP q3w starting on week 0 for 4 cycles. Non-PD patients who completed the 4 cycles of Durvalumab + EP will be randomized 1:1 into Arm 1 and Arm 2. Eligible patients should begin continuous treatment in 3 days after randomization. * Arm 1: Durvalumab 1500 mg monotherapy will be continued q4w. Anlotinib will be administered according to prescribing information in general use. The dose is 12mg, QD, PO, 14 days-on and 7 days-off. * N.B. If a patient's weight falls to 30 kg or below (≤30 kg) the patient should receive weight-based dosing equivalent to 20 mg/kg of durvalumab until the weight improves to \>30 kg, at which point the patient should start receiving the fixed dosing of durvalumab 1500 mg. Anlotinib is available at three dose levels, 12 mg, 10 mg, and 8 mg. Dose reduction may take place whenever toxicity that is not controlled with optimal supportive care is noted during the study. If a subject subsequently tolerates treatment well at that level in the judgment of the investigator, the dose may be increased to the next dose level. If a subject cannot tolerate treatment after dose reduction to 8 mg, treatment will be discontinued. * Arm 2: Durvalumab 1500 mg monotherapy will be continued q4w.