Clinical Outcomes of Second-Line Amrubicin and Platinum-Based Doublet Chemotherapy in Patients with Extrapulmonary Neuroendocrine Carcinoma: A Multicenter Retrospective Study

Background/Objectives: Extrapulmonary neuroendocrine carcinoma (EPNEC) is a rare, heterogeneous malignancy with no standard second-line treatment after progression on first-line platinum-doublet chemotherapy. We compared the efficacy and safety of amrubicin (AMR) versus platinum-based doublet as second-line therapy for advanced EPNEC. Methods: This multicenter retrospective study included patients with advanced EPNEC treated at five Japanese institutions who received second-line AMR or a platinum-based doublet. Overall survival (OS), progression-free survival (PFS), objective response rate (ORR), disease control rate (DCR), and adverse events were assessed. Results: Forty-four patients were enrolled (platinum-based doublet, n = 25; AMR, n = 19). Median OS was 6.1 months (95% confidence interval [CI], 4.9–9.0) and 6.8 months (95% CI, 2.7–13.2), and median PFS was 2.2 months (95% CI, 1.6–4.4) and 2.1 months (95% CI, 1.5–6.8), respectively. ORR and DCR were 20.0% and 32.0% in the platinum group and 5.3% and 26.3% in the AMR group, respectively. No significant differences were observed for OS, PFS, ORR, or DCR. Grade 3–4 hematologic toxicity was more frequent in the platinum group, whereas severe non-hematologic toxicity was rare in both groups. Conclusions: AMR therapy and platinum-based doublet therapy may exhibit comparable efficacy and acceptable safety profiles as second-line treatment options for advanced EPNEC.