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KEY CONCEPTS

  • Small bowel neoplasms are rare with roughly 12,000 new cases per year in the United States. The two most common histologies are adenocarcinoma (30%–40%) and carcinoid tumors (40%–45%).

  • Inflammatory bowel disease, Peutz-Jeghers, familial adenomatous polyposis, celiac disease, and hereditary nonpolyposis colorectal cancer and all increase the risk of developing small bowel adenocarcinomas.

  • Surgery is the mainstay of curative therapy; however, patients often present with more advanced disease, especially with adenocarcinomas.

  • There is no firmly established adjuvant therapy for patients with either carcinoid tumors or adenocarcinoma.

  • Systemic therapy for patients with advanced disease mirrors treatment for neuroendocrine tumors for carcinoids, whereas FOLFOX (modified 5-fluorouracil and oxaliplatin), CAPOX, and regimens with irinotecan are active for patients with adenocarcinoma.

  • The molecular defects in adenocarcinomas are being elucidated. To date, however, no targeted therapy has an established role in advanced disease. Mismatch repair defects (even more frequent than in colorectal cancer) are predictive of response to immune checkpoint blockade.

  • Appendiceal neoplasms are very rare consist of two major types: appendiceal carcinoid tumors and appendiceal epithelial tumors, each accounting for roughly half all cases.

  • No clear risk factors for appendiceal neoplasms have been identified.

  • Surgery is the mainstay of curative therapy for all patients with appendiceal neoplasms. Patients with adenocarcinomas are more likely to present with advanced disease in comparison with those with carcinoid tumors.

  • The histologic subtypes of epithelial appendiceal neoplasms include low- and high-grade appendiceal mucinous neoplasms and invasive adenocarcinomas that may be mucinous (low or high grade), nonmucinous, or with signet ring cell features.

  • Metastatic low-grade mucinous tumors have a more indolent disease course, respond poorly to systemic therapy, and are primarily managed with surgical cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC).

  • Metastatic high-grade adenocarcinomas, which include all tumors with signet ring cell features, are often treated with systemic chemotherapy. The benefit from cytoreductive surgery and HIPEC is uncertain.

SMALL BOWEL CANCER

Small bowel cancer is a rare malignancy representing approximately 3% of gastrointestinal (GI) neoplasms.1 In 2020, it was estimated that 11,110 new cases of small bowel cancer and 1700 small bowel cancer–related deaths would occur.1 The two most common histologies seen in cancers of the small intestine are carcinoids and adenocarcinomas.2 Because of the nonspecific clinical presentation of small bowel adenocarcinoma (SBA) and the difficulty in imaging the small bowel, most patients with SBA present with lymph node involvement or distant metastases. Even in patients with localized disease who undergo resection with curative intent, the prognosis is poor, and no studies have yet demonstrated a clear benefit from adjuvant therapy. However, there have been some recent advances in molecular profiling as well as the use of chemotherapy, targeted therapy, and immunotherapy as palliative treatments. In this chapter, the epidemiology, diagnosis, and treatment of small bowel cancers, in particular SBA, are reviewed.

Epidemiology

Based on an analysis of the Surveillance, Epidemiology, and End Results (SEER) database, the age-adjusted ...

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