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1. SMALL INTESTINAL ADENOCARCINOMAS

These are aggressive tumors that occur most commonly in the duodenum or proximal jejunum. The incidence is rare, with 10,470 new diagnoses estimated in 2018 in the United States. Overall, prognosis is poor, with 5-year survival of 85% for localized disease, 75% for regional disease, and 42% for distant disease (overall, 27% of patients are stage IV at diagnosis). The management of small intestinal adenocarcinoma is extrapolated from data available for the management of colon adenocarcinoma. The ampulla of Vater is the most common site of small bowel carcinoma. 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. Adjuvant chemotherapy with gemcitabine or 5-fluorouracil was associated with a significantly better overall median survival benefit compared to observation alone (43.1 vs 35.2 months, respectively) in patients with resected periampullary adenocarcinoma.

Nonampullary adenocarcinomas of the small intestine account for less than 3% of all gastrointestinal cancers but comprise approximately one-third of small bowel cancers. Peak incidence is in the sixth decade. Most cases 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 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. They occur most commonly in the small intestine. 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. 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 the setting of immunoproliferative small intestinal disease. In this condition, there is diffuse ...

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