A rare and slow-growing form of cancer, carcinoid tumors may develop anywhere in the body where neuroendocrine (hormone-producing) cells exist. Roughly 75% of carcinoids arise in the gastrointestinal (GI) tract, particularly the small intestine. Another 24% occur in the lung and the remaining 1% occur everywhere else.
Since carcinoid tumors often exist for years without yielding symptoms, early diagnosis is difficult. The tumors frequently are not discovered until they become large enough to cause discomfort, but they can be found during an exam when the doctor is looking for something unrelated, or during a surgery for another digestive system condition.
Although accurate statistics for carcinoid tumors are not readily available, it is estimated that roughly two out of every 100,000 people develop carcinoid tumors.