Medical condition
Small intestine cancer is a cancer of the small intestine. It is relatively rare compared to other gastrointestinal malignancies such as gastric cancer (stomach cancer) and colorectal cancer.
Small intestine cancer can be subdivided into duodenal cancer (the first part of the small intestine) and cancer of the jejunum and ileum (the latter two parts of the small intestine). Duodenal cancer has more in common with stomach cancer, while cancer of the jejunum and ileum have more in common with colorectal cancer. Five-year survival rates are 65%.
Experts believe that small intestine cancer develops much like colorectal cancer. It first begins as a small growth on the inner lining of the intestine (polyp), which over time becomes cancer. 
Approximately 50% of adenomas of the small intestine arise in the duodenum even though this location comprises only 4% of the length of the small intestine. These adenomas occur mainly close to the ampulla of Vater, the outlet of the common bile duct from which bile acids are released. This area is also closely associated with the pancreas, so they are treated as pancreatic cancer.
The small intestine works by mixing food and gastric juices into a thick fluid in the stomach and then emptied into the small intestine. It then continues to break down and absorb the nutrients. Although it is referred to as the small intestine, it is the longest section of the GI tract being approximately 20 feet long. The length of the small intestine comprises 75% of the length of the entire gastrointestinal tract
There are three parts of the small intestine. The duodenum is the 1st section of small intestine and only about a foot long. The jejunum and ileum make up most of the small intestine. Most of the nutrients in food are absorbed into the bloodstream in these two parts. 
Histopathologic types.
Subtypes of small intestine cancer include:
Most small intestine cancers (especially adenocarcinomas) develop in the duodenum. Cancers developed in the duodenum are often found at the ampulla of Vater. (American Cancer Society, 2023)
Risk factors.
Risk factors for small intestine cancer include:
References.
 ;templatestyles src="Reflist/styles.css" / ;
American Cancer Society. (2023). "Key statistics for small intestine cancer". American Cancer Society. Retrieved April 3, 2023, from [URL] 
Cleveland Clinic. (2022). "Small intestine cancer: Symptoms, causes, Prognosis &amp; Treatment". Cleveland Clinic. Retrieved April 4, 2023, from [URL] 
Markman, M. (2022, July 20). "Intestinal cancer: Causes, symptoms &amp; treatments". Cancer Treatment Centers of America. Retrieved April 4, 2023, from [URL] 
Radhakrishnan, R. (2021, May 6). "Is small intestine cancer curable?" MedicineNet. Retrieved April 4, 2023, from [URL] 