PurposeTo evaluate the safety, tolerability, and preliminary efficacy of multiple doses of pegylated irinotecan (JK1201I) as a second-line monotherapy for treating small-cell lung cancer (SCLC) patients. MethodsAccording to the "3 + 3" dose-escalation principle, patients received intravenous JK1201I at 180 or 220 mg/m2 once every 3 weeks for four cycles. Progression-free survival (PFS), overall survival (OS), median progression-free survival (mPFS), and median overall survival (mOS) were evaluated. The Kaplan-Meier method was used to analyze PFS and overall OS. Brookmeyer and Crowley's method was used for mPFS and mOS. ResultsThis study included 29 patients with stage III-IV SCLC (stage IIIa, n = 1; stage IIIb, n = 1; and stage IV, n = 27). Of these, 26 patients were enrolled in the 180 mg/m(2) dose group, and 3 patients were enrolled in the 220 mg/m(2) dose group. No dose-limiting toxicity (DLT) was noted during the first 28 days of treatment. Grade 3 or higher adverse events were recorded in the 180 mg/m(2) group, including diarrhea (11.5%, 3/26), neutropenia (7.7%, 2/26), and leukopenia (7.7%, 2/26). In the 220 mg/m(2) group, one patient (33.3%, 1/3) experienced neutropenia or leukopenia. In the 180 mg/m(2) group, 38.5% (10/26) of patients achieved an objective response rate (ORR), with a disease control rate (DCR) of 73.1% (19/26). The mPFS and mOS were 3.4 and 12.1 months, respectively. In the 220 mg/m2 group, one patient had stable disease, and one had progressive disease (PD). The ORR, DCR, mPFS, and mOS were 0% (0/3) and 33.3% (1/3), 2.7 months and 2.7 months, respectively. ConclusionJK1201I exhibits promising efficacy and relatively low toxicities as a second-line monotherapy for SCLC, warranting further large-scale clinical studies to evaluate its efficacy in greater detail.