Pancreatic neuroendocrine tumors (PNETs) were considered an extremely rare disease. However, in recent years, the number of patients with PNET has increased rapidly. According to an epidemiological survey conducted in Japan, the number of treated patients with PNETs in 2010 was approximately 1.2-times that in 2005, and the number of new incidences of non-functional PNETs in 2010 was approximately 1.7-times that in 2005. Among functional PNETs, insulinoma was most prevalent, followed by gastrinoma. To diagnose PNETs, correct histological diagnosis is most important. According to the World Health Organization 2010 classification criteria, neuroendocrine tumors (NETs) are categorized into well-differentiated NETs and poorly differentiated neuroendocrine carcinomas (NECs). NECs accounted for 7.6% of all NETs, and functional and non-functional PNETs accounted for 2.1% and 10.1%, respectively. Patients with distant metastasis accounted for 19.9%, and those with multiple endocrine neoplasia type 1 accounted for 4.3%. When treating PNETs, it is necessary to correctly evaluate the functionality and progression of tumors, the presence or absence of metastasis, and the degrees of differentiation and malignant potential of tumors. A new registration system from the Japan Neuroendocrine Tumor Society will start to be used in 2015, which will help further dissemination of Japanese epidemiological information to the world.
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