Symptoms are unusual in the early stages. When symptoms do occur, the tumor has already spread in 90 percent of patients. The most common symptoms are periodic abdominal pain, intermittent intestinal obstruction and kinking of the bowel. Gastrointestinal bleeding is uncommon and ulcerations of the tumor are rare.
In addition to the symptoms caused by the tumor, there may be symptoms of the carcinoid syndrome. This is characterized by facial flushing, wheezing, diarrhea and cardiac valvular disease. It is caused by abnormal amounts of the two hormones produced by malignant carcinoids, serotonin and substance P, and other biologically active substances. The syndrome occurs in about 10 percent of patients with carcinoid tumor, almost always because of carcinoid metastases in the liver.
