Recent epidemiology of patients with gastro-entero-pancreatic neuroendocrine neoplasms (GEP-NEN) in Japan: a population-based study

Background The worldwide prevalence and incidence of neuroendocrine neoplasms (NEN) have been increasing recently, although few studies have analyzed data on the current situation of NENs in Japan. Here, the Japan Neuroendocrine Tumor Society (JNETS) planned to investigate the recent incidence and distribution of these tumors using data from the national cancer registry started in 2016. This study examined the incidence and distribution of primary sites as well as rate of advanced disease from this population-based registry. Methods A retrospective, population-based study using data from the national cancer registry in Japan (NCR) was conducted to evaluate patients with gastro-entero-pancreatic NEN (GEP-NEN) in 2016. Associated population data were used to determine annual age-adjusted incidences. Results A total of 6735 individuals were diagnosed with GEP-NEN in Japan in 2016. Annual onset incidence was 0.70/100,000 for pancreatic NEN and 2.84/100,000 for gastrointestinal NEN. NEN in the ileum accounted for only 1% of total GEP-NENs in Japan. Most NENs in the esophagus or lungs were neuroendocrine carcinomas (NECs), while the majority of those in the duodenum, ileum, appendix and rectum were grade 1 neuroendocrine tumors (NETs). Median age at initial diagnosis was in between 60 to 65. Tumors in the duodenum, appendix and rectum were mostly limited to local, while those in the esophagus, stomach and colon tended to show distant metastasis. In Japan, initial treatment for GEP-NENs was resection even if the tumor was NEC. Conclusions This is the first report of a national registry-based incidence and distribution of GEP-NEN in Japan. These data will serve as an important first step to determining the exact etiology and trends for this pathology in Japan.