Inclusion criteria:

          1. Histologically or cytologically documented limited-stage small cell lung cancer (stage
             I-III).

          2. Received 4 cycles of chemotherapy concurrent with radiotherapy, which must be
             completed within 1 to 42 days prior to randomization and the first dose of IP.
             Chemotherapy must contain platinum and IV etoposide. Radiotherapy must be either total
             60-66 Gy over 6 weeks for the standard QD regimen or total 45 Gy over 3 weeks for
             hyperfractionated BD schedules.

          3. PCI may be delivered at the discretion of investigator and local standard of care, and
             must be conducted after the end of cCRT and completed between 1 to 42 days to first
             dose of IP.

        4 .Have not progressed following definitive concurrent chemoradiation 5 .Life expectancy ≥
        12 weeks at Day 1. 6. ECOG 0 or 1 at enrolment.

        Exclusion criteria:

          1. Extensive-stage SCLC

          2. Active or prior documented autoimmune or inflammatory disorders

          3. Uncontrolled intercurrent illness, including but not limited to interstitial lung
             disease.

          4. Active infection including tuberculosis, HIV, hepatitis B and C

          5. Patients who received sequential chemotherapy and radiotherapy (no overlap of RT with
             chemotherapy)