Purpose: Amrubicin, a third-generation anthracycline and potent topoisomerase II inhibitor, showed promising activity in small-cell lung cancer (SCLC) in phase II trials. This phase III trial compared the safety and efficacy of amrubicin versus topotecan as second-line treatment for SCLC. Patients and Methods: A total of 637 patients with refractory or sensitive SCLC were randomly assigned at a ratio of 2:1 to 21-day cycles of amrubicin 40 mg/m2 intravenously (IV) on days 1 to 3 or topotecan 1.5 mg/m2 IV on days 1 to 5. Primary end point was overall survival (OS); secondary end points included overall response rate (ORR), progression-free survival (PFS), and safety. Results: Median OS was 7.5 months with amrubicin versus 7.8 months with topotecan (hazard ratio [HR], 0.880; P = .170); in refractory patients, median OS was 6.2 and 5.7 months, respectively (HR, 0.77; P = .047). Median PFS was 4.1 months with amrubicin and 3.5 months with topotecan (HR, 0.802; P < .018). ORR was 31.1% with amrubicin and 16.9% with topotecan (odds ratio, 2.223; P < .001). Grade ��� 3 treatment-emergent adverse events in the amrubicin and topotecan arms were: neutropenia (41% v 54%; P = .004), thrombocytopenia (21% v 54%; P < .001), anemia (16% v 31%; P < .001), infections (16% v 10%; P = .043), febrile neutropenia (10% v 3%; P = .003), and cardiac disorders (5% v 5%; P = .759); transfusion rates were 32% and 53% (P < .001), respectively. NQO1 polymorphisms did not influence safety outcomes. Conclusion: Amrubicin did not improve survival when compared with topotecan in the second-line treatment of patients with SCLC. OS did not differ significantly between treatment groups, although an improvement in OS was noted in patients with refractory disease treated with amrubicin.