Nationwide real-world analysis of extrapulmonary neuroendocrine carcinomas in Japan using the JMDC claims database

Neuroendocrine carcinomas (NECs) are biologically aggressive, high-grade malignancies that differ fundamentally from well-differentiated neuroendocrine tumors. NECs are managed primarily with cytotoxic chemotherapy, and therapeutic options remain limited. Real-world data on the clinical characteristics and treatment patterns of NECs in Japan are scarce. We conducted a retrospective observational study from January 2014 to November 2024 using the Japan Medical Data Center (JMDC) claims database, which contains anonymized health insurance claims from insured individuals across Japan. Patients with extrapulmonary NECs (expNECs) were identified using predefined disease codes combined with treatment and procedure records. Patient demographics, primary tumor sites, and treatment modalities, including surgery and chemotherapy, were analyzed. Overall survival was estimated using the Kaplan–Meier method and compared across disease stages. A total of 1,193 patients (women: 319, men: 874) with expNECs were identified in the JMDC database. Men accounted for a higher proportion of expNEC cases than women. The mean age at diagnosis of expNEC was 71 ± 11 years and was lower in women (68 ± 13 years) than in men (71 ± 11 years). The number of expNEC cases identified in the database increased over time. ExpNECs arose predominantly in the stomach and colorectal. Most patients were diagnosed at advanced stages (Stages III and IV). Surgical treatment combined with cytotoxic chemotherapy was commonly employed, with platinum-based regimens being the most frequently administered. In the subset of patients with available TNM stage information, overall survival differed significantly across Stage I–IV disease in the overall expNEC cohort and in colorectal and gastrointestinal NECs (all p < 0.001), but not in gastric NEC, with marked survival impairment in Stages III and IV. Our nationwide claims-based analysis delineates the real-world clinical profile and treatment patterns of expNECs in Japan. Within the limitations of claims data, expNECs are characterized by advanced-stage presentation and predominant reliance on platinum-based chemotherapy.