Compared to countries other than Japan, the frequency of rectal NETs among gastrointestinal NETs is high in Japan, whereas the frequency of midgut NETs is high in Europe and the U.S. In addition, the frequency of MEN1 in cases of pancreatic NET is lower in Japan than that in Europe and the U.S. Accordingly, diagnostic and treatment approaches differ between patients from Japan and Europe or the U.S., requiring specific guidelines for patients in Japan. Here, MEN1 is linked to digestive system neuroendocrine tumor, grade 1/2.