The frequency of different tumor types varies by location within the small intestine. Adenocarcinomas are most common in the duodenum and jejunum and neuroendocrine tumors, in the ileum. Lymphomas and sarcomas each have similar incidences in the various segments of the small intestine.
1. SMALL INTESTINAL ADENOCARCINOMAS
These tumors often present with nonspecific symptoms such as abdominal pain and nausea. The incidence is rare, with 11,110 new diagnoses estimated in 2020 in the United States. These adenocarcinomas are most often diagnosed at stage III or IV, but their prognosis is slightly worse than for similar stage colon adenocarcinoma. The duodenum is the most common site of small bowel adenocarcinoma, specifically in the periampullary region. The incidence of ampullary carcinoma is increased more than 200-fold in patients with familial adenomatous polyposis. Periodic endoscopic surveillance to detect early ampullary neoplasms is therefore recommended. Ampullary carcinoma may present with jaundice due to bile duct obstruction or bleeding. Surgical resection of early lesions is curative in up to 40% of patients. Although ampullary adenocarcinomas may be of either intestinal or pancreatic ductal origin, adjuvant chemotherapy with a pancreatic regimen is typically recommended and is associated with improved overall survival compared to observation alone.
The management of nonampullary small intestinal adenocarcinoma is extrapolated from data available for the management of colon adenocarcinoma. Most cases of nonampullary adenocarcinomas present with symptoms of obstruction, acute or chronic bleeding, or weight loss. Resection is recommended for control of symptoms. The benefit of adjuvant therapy after resection of stage II or III tumors is unclear but it is generally administered using chemotherapy agents active in colorectal cancer. Patients with Crohn disease have an increased risk of small intestine adenocarcinoma, most commonly in the ileum; it may be difficult to distinguish preoperatively from disease-related fibrous stricture. Small bowel adenocarcinoma in young patients or those with a family history of gastrointestinal or extracolonic adenocarcinomas should prompt screening for the Lynch syndrome. In this syndrome, there is an increased risk of small bowel adenocarcinomas, occurring in approximately 4–8% of affected patients. According to NCCN guidelines, periodic surveillance with esophagogastroduodenoscopy (EGD) and extended duodenoscopy or capsule endoscopy may be considered for patients with Lynch syndrome, although there are no randomized trials to support such small bowel screening.
2. SMALL INTESTINAL LYMPHOMAS
Lymphomas may arise primarily in the gastrointestinal tract or may involve it secondarily in patients with disseminated disease. In Western countries, primary gastrointestinal lymphomas account for 5% of lymphomas and 20% of small bowel malignancies. There is an increased incidence of small intestinal lymphomas in patients with AIDS, Crohn disease, and those receiving immunosuppressive therapy. The most common histologic subtype is non-Hodgkin extranodal marginal zone (MALT) B-cell lymphoma. That said, enteropathy-associated T-cell lymphomas appear to be increasing in incidence in the United States. They are associated with the diagnosis of celiac disease. In the Middle East, lymphomas may arise in ...