Definition

A rare cancer that forms in tissues of the small intestine (a long tube-like organ that connects the stomach to the large intestine). The most common type of small intestine cancer is adenocarcinoma (cancer that begins in cells that make and release mucus and other fluids). Other types of small intestine cancer include leiomyosarcoma (cancer that begins in the smooth muscle cells of the small intestine), gastrointestinal (GI) neuroendocrine tumor (a slow-growing type of cancer that begins in the lining of the GI tract), GI stromal tumor (a type of tumor that usually begins in cells in the wall of the GI tract), and lymphoma (cancer that begins in immune system cells).