This is an open-label, single-arm, prospective phase 2 study, evaluating the efficacy and safety of ivonescimab combined with irinotecan liposome for relapsed small cell lung cancer, who progressed on PD-(L)1 -based first-line therapy.

Patients will receive ivonescimab at 20 mg/kg intravenously, on days 1 of every 21-day cycle and irinotecan liposome 56.5mg/m^2 intravenously, on days 1 of every 14-day cycle. Treatment will be discontnued in case of the toxicity became intolerable, the investigator determined that there was no further clinical benefit (based on a combination of RECIST 1.1 imaging assessment and clinical status), 24 months of treatment was completed, or the study was withdrawn for other reasons.

Inclusion Criteria:

1. 18 to 75 years old (at the time of inform consent obtained).
2. Be able and willing to provide written informed consent and to comply with all requirements of study participation (including all study procedures).
3. Histologically confirmed SCLC (per the Veterans Administration Lung Study Group [VALG] staging system).
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
5. Life expectancy of at least 3 months.
6. ES-SCLC who failed first-line platinum-based chemotherapy with checkpoint inhibitors.
7. At least one measurable tumor lesion according to RECIST v1.1.
8. Adequate organ function.
9. 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:

1. Patients with other cancer in 5 years.
2. Undergone anti-angiogenic therapy prior to the first dose of study treatment.
3. Evidence and history of severe bleeding tendency.
4. History of severe active autoimmune disease that has required systemic treatment in the past 2 years, severe drug allergy or have known allergy to any component of the study drugs.
5. Active central nervous system (CNS) metastases.
6. Active infection requiring systemic therapy.
7. Current presence of uncontrolled pleural, pericardial, and peritoneal effusions.
8. Active hepatitis B/C, or HIV infection.
9. History of myocardial infarction, unstable angina, cardiac or other vascular stenting, angioplasty, or surgery within 12 months prior to day 1 of study treatment.
10. History of allogeneic hematopoietic stem cell transplantation or allogeneic organ transplantation.
11. History of alcohol abuse, psychotropic substance abuse or drug abuse.
12. Pregnant or lactating women.
13. Other conditions considered unsuitable for this study by the investigator.