A rare case of metachronous neuroendocrine tumor after a colorectal adenocarcinoma: qualitative critical review of synchronous and metachronous gastrointestinal NET

Gastrointestinal neuroendocrine tumor (NET) associated with a metachronous intestinal adenocarcinoma is rare. We report the case of a 71-year-old man with an ileal NET. Patient has previously undergone a left colectomy for sigmoid cancer. We report a complete review both of the metachronous and synchronous NET. A comprehensive systematic literature search in PubMed, EMBASE, and MEDLINE identified a total of 35 relevant studies. This study includes an analysis of review articles, case reports, case series, retrospective studies and population-based studies. In the English literature to date, there are 21 case reports (19 synchronous cases and 2 metachronous cases), 3 case series and 3 review articles, and less than 10 retrospective studies or population-based studies. A total of 31 patients in 24 articles were included in the study: 28 patients with a synchronous gastrointestinal NET and colorectal adenocarcinoma and 3 patients with metachronous gastrointestinal NET and colorectal adenocarcinoma. The incidence of synchronous cancer (particularly for colorectal and gastric cancer) with a gastrointestinal NET ranges from 10 to 50%, while for the metachronous ones it is still unclear. This is the third metachronous case report and the first descriptive case of gastrointestinal NET diagnosed 2 years after a colorectal adenocarcinoma. An endoscopic follow-up program for gastrointestinal NET patients and/or for first-degree relatives of NET patients appears recommendable.