⁃ Patients must meet all of the following inclusion criteria to be enrolled:

• Male or female with age ≥ 18 years old at the time of informed consent.

• Histologically or cytologically confirmed LS-SCLC using the Veteran's Administration Lung Study Arm (VALSG) staging criteria (Appendix 3). Patients with TNM Stage I or II disease per AJCC 8th edition must be medically inoperable (as determined by the Investigator) or the patient must refuse surgery.

• Received CRT defined as: (1) 4 cycles of chemotherapy consisting of carboplatin or cisplatin and intravenously administered etoposide; (2) a total radiation dose of 60-66 Gy for the standard once daily (QD) radiotherapy regimen or 45 Gy for the hyperfractionated twice daily (BID) radiotherapy regimen; (3) Patients must begin investigational interventions within 42 days of the last dose of chemotherapy.

• Patients must have achieved a complete response (CR), partial response (PR), or stable disease (SD) after receiving curative platinum-based CRT and must not have developed progressive disease (PD) prior to study entry.

• Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0-1 .

• Adequate organ function

• Female patients of childbearing potential and male patients whose partners are women of childbearing age.

• Voluntarily agree to participate in the study, sign the informed consent form, and agree to comply with all study and follow-up procedures.