A Phase Ib/III Clinical Study to Evaluate the Efficacy and Safety of IBI318 in Combination With Paclitaxel Versus Placebo in Combination With Paclitaxel in Patients With Small Cell Lung Cancer Who Have Failed First-line or Above Chemotherapies

Inclusion Criteria:

1. Signed the Informed Consent Form;
2. Male or female ≥ 18 and≤75 years of age;
3. Life expectancy ≥ 12 weeks;
4. Pathologically confirmed limited or extensive stage small cell lung cancer according to Veterans Lung Administration Lung Study Group (VALG) staging;
5. At least had progressive disease during or after platinum-based first-line chemotherapy or chemoradiotherapy, and with clear evidence of radiographic progression.

Exclusion Criteria:

1. Previous exposure to immune-mediated therapy; previous use of taxane chemotherapy;
2. Received the last anti-tumor therapy (chemotherapy, radiotherapy) within 4 weeks prior to the first dose of study drug;
3. Received any investigational agent within 4 weeks prior to the first dose of study drug;
4. Received systemic treatment with Chinese herbal medicine indicated for cancer or drugs used for immunoregulation (including thymosin, interferon, interleukin, except for local use for pleural effusion) within 2 weeks before the first dose;
5. Are participating in another interventional clinical study, or observational (non-interventional) clinical study or in the follow-up phase of an interventional study;
6. Pregnant or breastfeeding woman.