Carcinoid tumors are a type of slow-growing cancer that typically arise in the gastrointestinal tract, particularly in the small intestine, appendix, and rectum. They can also develop in other areas, such as the lungs. These tumors originate from neuroendocrine cells, which produce hormones that can affect various bodily functions. Many carcinoid tumors do not cause symptoms in their early stages. However, when they do produce hormones, they can lead to a condition known as carcinoid syndrome, characterized by flushing, diarrhea, and wheezing. Diagnosis often involves imaging tests and blood tests to measure hormone levels.