Because carcinoid tumors usually start out very small and grow and spread slowly, about half of all gastrointestinal carcinoid tumors are found in an early or localized stage, often before they cause any problems.
Carcinoid tumors often are found by accident. These tumors aren’t causing any symptoms but are found when tests are done for other reasons or diseases. They may also be found when parts of the gastrointestinal system are removed to treat other diseases. When patients have parts of their stomach or small intestine removed to treat other diseases, taking a close look in the microscope often shows small groups of neuroendocrine cells that look like tiny carcinoid tumors. Researchers still do not know why some tumors stay small, but others grow large enough to cause symptoms.
For example, a person with stomach pain or bleeding may have a test called an upper endoscopy to look for an ulcer. In this test, the doctor looks at the stomach lining through a flexible lighted tube. During this test, the doctor might notice a small bump in the stomach wall that turns out to be a carcinoid tumor.
Sometimes during colorectal cancer screening, a routine sigmoidoscopy, or colonoscopy (looking at the large bowel through a flexible lighted tube) will incidentally find a small carcinoid tumor.
Sometimes when the appendix is removed (to treat appendicitis or as part of a larger operation), a small carcinoid tumor is found at the tip. This happens in about 1 of every 300 people who have appendix surgery. Most of these carcinoids were too small to have caused any symptoms.
Strosberg JR. Clinical characteristics of well-differentiated neuroendocrine (carcinoid) tumors arising in the tubular digestive tract, lung, and genitourinary tract. UpToDate website. https://www.uptodate.com/contents/clinical-characteristics-of-well-differentiated-neuroendocrine-carcinoid-tumors-arising-in-the-tubular-digestive-tract-lung-and-genitourinary-tract?search=GI%20carcinoid&source=search_result&selectedTitle=4~150&usage_type=default&display_rank=4#H15. Updated Oct. 20, 2017. Accessed Aug. 2, 2018.