A Study of AK104 in Combination With Chiauranib in Patients With Extensive Stage Small Cell Lung Cancer

Inclusion Criteria: 1. The subject must sign the written informed consent form (ICF) voluntarily. 2. Aged ≥ 18 to ≤ 75 years. 3. Eastern Cooperative Oncology Group(ECOG) performance status score of 0 or 1. 4. Life expectancy≥ 3 months. 5. Histologically or cytologically confirmed ES-SCLC according to the Veterans Administration Lung Study Group(VALG) stage. 6. Phase Ib and II: Subjects with ES-SCLC who have failed prior first-line platinum-based chemotherapy in combination with PD1/PDL1 inhibitors will be enrolled. 7. At least 1 measurable lesion per RECIST v1.1, which is applicable for repeated accurate measurement. Brain metastatic lesions are not considered target lesions. 8. Adequate organ function. 9. Women of childbearing potential must have a negative urine or serum pregnancy test 10. If a nonsterile male subject has sexual intercourse with a female partner of childbearing potential, he must use an effective method of contraception from the start of screening until Day 120 after the last dose; it should be discussed with the Investigator whether contraception should be discontinued after this time point. 11. Subjects must be willing and able to comply with the scheduled visits, treatment regimens, laboratory tests, and other requirements in the study. Exclusion Criteria: 1. Malignancies other than SCLC within 3 years prior to enrollment. However, subjects with other malignancies that have been cured are eligible. 2. Concurrent enrollment in another clinical study, unless it is an observational, non-interventional clinical study or a follow-up period of an interventional study. 3. Subjects whose imaging at screening shows that the tumor encircles important blood vessels or has significant necrosis and cavitation, and the subjects'participation is associated with a risk of hemorrhage. 4. Tumor invasion of surrounding vital organs and blood vessels. 5. Subjects who had active autoimmune disease that required systemic treatment in the past two years. 6. Subjects with prior history of non-infectious pneumonitis/interstitial lung disease requiring systemic glucocorticoid therapy or with non-infectious pneumonitis at present. 7. Presence of metastases to brainstem, meninges and spinal cord, or spinal cord compression. 8. Subjects with pleural effusion, pericardial effusion, or ascites that are clinically symptomatic or require drainage. 9. Subjects with unresolved toxicity due to prior anti-tumor therapy, defined as failure to recover to National Cancer Institute Common Terminology Criteria for Adverse Events(NCI CTCAE) v5.0 Grade 0 or 1 (except for alopecia) or to the levels specified in the inclusion/exclusion criteria. 10. Subjects who cannot swallow pills, and who have malabsorption syndrome, or any condition affecting gastrointestinal absorption. Subjects with active or prior history of definite inflammatory bowel disease. 11. Subjects with a history of immunodeficiency; a positive human immunodeficiency virus (HIV) antibody test; and current long-term use of systemic corticosteroids or other immunosuppressants. 12. Known history of allogeneic organ transplantation and allogeneic hematopoietic stem cell transplantation. 13. Subjects who had major surgical procedure or serious trauma within 30 days prior to the first dose, or a major scheduled surgery within 30 days after the first dose; subjects who had minor local surgery within 3 days prior to the first dose.