This Phase II study was designed to evaluate the safety and efficacy of irinotecan in combination with simvastatin compared with treatment with irinotecan alone in ES-SCLC patients relapsed from first-line chemotherapy. Participants will be divided in a 1:1 ratio to receive either irinotecan (4 cycles) + simvastatin (10 months) or irinotecan (4 cycles) until progressive disease (PD) as assessed by the investigator using Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v1.1). Treatment can be continued until persistent radiographic PD or symptomatic deterioration.

PRIMARY OBJECTIVES:

I.To evaluate the progression-free survival (PFS) of patients with extensive stage-small cell lung cancer (ES-SCLC) treated with irinotecan + simvastatin or with irinotecan alone.

SECONDARY OBJECTIVES:

I.To assess best overall response rate (ORR) after treatment. II.To assess disease control rate (DCR) after treatment.

III.To estimate overall survival (OS) of patients with ES-SCLC. IV. To evaluate the toxicity profile of irinotecan + simvastatin.

EXPLORATORY OBJECTIVES:

I.To evaluate biomarkers correlatives. II.To explore the mechanism of irinotecan + simvastatin in the treatment of chemotherapy-resistant participants with ES-SCLC.

OUTLINE: Patients are divided into two arms. ARM A: Participants received intravenous infusions of irinotecan 60 milligrams per square meter (mg/m^2) on Day 1,8 of every 21-day cycle (4 cycles) in combination with oral simvastatin (40mg daily) （10 months）until persistent radiographic PD, symptomatic deterioration, intolerable toxicity, withdrawal of consent, death, or study termination by the Sponsor.

ARM B:Participants received intravenous infusions of irinotecan 60 milligrams per square meter (mg/m^2) on Day 1,8 of every 21-day cycle (4 cycles) until persistent radiographic PD, symptomatic deterioration, intolerable toxicity, withdrawal of consent, death, or study termination by the Sponsor.

Inclusion Criteria:

Patients must be volunteered to participate in the clinical trial. Patients must sign the informed Consent form (ICF) and be willing to follow and be able to complete all test procedures.

Histologically or cytologically confirmed ES-SCLC (per the Veterans Administration Lung Study Group [VALG] staging system).

No patients with resectable or radical radiotherapy lung cancer. Patient must have no Epidermal Growth Factor Receptor (EGFR) mutation, Anaplastic lymphoma kinase (ALK) rearrangement, or ROS proto-oncogene 1 , receptor tyrosine kinase(ROS1) rearrangement.

Patient must be at least resistant to the first-line chemotherapy. Patients must have measurable disease based on Response Evaluation Criteria in Solid Tumors (RECIST) 1.1.

Patients can tolerate chemotherapy.

Exclusion Criteria:

Unclear diagnosis of SCLC. Resectable or radical radiotherapy SCLC. Contraindicated chemotherapy. Undergoing other active malignancies within 5 years or at the same time.Patients with localized curable tumors, such as basal cell carcinoma, squamous cell carcinoma, superficial bladder carcinoma, prostate carcinoma in situ, cervical carcinoma in situ, or breast carcinoma in situ, will not be excluded.

Positive test result for human immunodeficiency virus (HIV). Positive test result for active tuberculosis. Live vaccine was administered within 28 days of initial administration. Inactivated viral vaccines for seasonal influenza are allowed, except for live attenuated intranasal vaccines.

Pregnant or lactating women. A history of psychotropic substance abuse, drug abuse, or alcoholism. Other factors assessed by the sponsors.

IPD is not available to other researchers.