There are three types of gastric carcinoid tumors that cause carcinoid syndrome. Tumors of the second type grow slowly and rarely become malignant. They prevail in patients with a genetic disorder such as multiple endocrine neoplasia. Not only the stomach, but also the pineal gland, thyroid gland, and pancreas can be affected. The third type of tumors are large tumors growing in a healthy stomach. They are malignant, penetrate deeply into the wall of the organ and give multiple metastases. May cause perforation and bleeding. TolThe colon is where carcinoid syndrome and carcinoid tumor are most often diagnosed. A photo of the mucous membrane during examination of this segment of the intestine shows the presence of large (five centimeters or more) tumors. They metastasize to regional lymph nodes and are almost always malignant.