The most striking feature is the bland monotous uniform appearance of the tumor without pleomorphism or mitotic activity. As with other endocrine tumors, prediction of aggressive biologic behavior is not possible on histologic grounds with the only absolute critieria being the presence of metastases. Carcinoids are slow growing low grade malignant tumors most of which do not metastasize and are asymptomatic at death. The most common symptom is non-specific abdominal pain, which has usually been present for a number of years. Bleeding is rare, and obstruction can occur due to size of the tumor, desmoplastic thickening of the intestinal wall, intestinal infarction secondary to mesenteric vessel compression by tumor, or intussusception.
Metastases first occur in regional nodes and then the liver.
The most striking presentation of these tumors is the Carcinoid Syndrome. The presence of the Carcinoid Syndrome indicates release of polypeptide hormones or vasoactive amines into the general circulation and in most cases denotes bulky hepatic metastases. The two most common symptoms of the Carcinoid Syndrome are flushing and diarrhea, and these are almost always associated with an elevated 5-HIAA, although the amines responsible for the symptoms are not clearly identified. Carcinoid tumors in other locations may secrete a variety of hormone products such as Gastrin, Insulin, ACTH, Somatostatin, VIP, etc. Robbins Pathologic Basis of Disease.