carcinoid of islet cells

Islet cell carcinoid is a tumor originating from EC cells, with the function of secreting hormones such as serotonin (5-HT) or 5-hydroxytryptophan (5-HTP). Some patients may clinically present with carcinoid syndrome. It is a low-grade malignant tumor with slow growth. As early as 1907, Oberndorfer first proposed that carcinoid is a slow-growing intestinal adenocarcinoma and introduced the term carcinoid. In 1953, Lembeck discovered serotonin in carcinoid tissue, which is the bioactive substance causing carcinoid syndrome. Williams classified carcinoids into foregut, midgut, and hindgut types. Foregut carcinoids secrete 5-HT, 5-HTP, vasoactive intestinal peptide, and polypeptide hormones, producing atypical carcinoid syndrome; midgut carcinoids, such as appendiceal carcinoids, secrete 5-HT and exhibit typical carcinoid syndrome; while hindgut carcinoids are mostly nonfunctional. Islet cell carcinoids differ from midgut carcinoids in that the presence of carcinoid syndrome does not necessarily indicate liver metastasis.