Very little is known about the causes of gastrointestinal carcinoid tumors. As with other cancers, scientists have recognized some changes in the DNA of carcinoid tumor cells that are probably responsible for their increased growth and abnormal spread. But, the causes of these changes are not yet known.
Physicians do know that carcinoid tumors start out very small and grow slowly.
When patients have parts of their stomach or small intestine removed to treat other diseases, close examination under the microscope often shows small groups of neuroendocrine cells that look like tiny carcinoids. Researchers still do not know why some remain so small and others begin to grow and become large enough to cause symptoms. Click here for information about prevention of gastrointestinal carcinoid tumors.