Small Intestine Cancer starts in cells of the small intestine (small bowel). The small intestine is part of the digestive system. It is a hollow, tube-like organ in the abdomen. The small intestine is about 6 m (20 ft) long. Its principal purpose is to absorb and digest nutrients. The small intestine makes up more than 70 % of the length and 90% of the surface of the gastrointestinal (GI) tract. The most common cancerous tumors of the small intestine are: lymphoma, sarcoma, carcinoids and adenocarcinoma.