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Neuroendocrine tumors (NETs) originate from enterochromaffin cells distributed throughout the body. This chapter focuses on low- to intermediate-grade gastroenteropancreatic NETs (GEP-NETs), although the term neuroendocrine tumor also denotes diseases such as small cell carcinoma, medullary thyroid carcinoma, neuroblastoma, and Merkel cell tumor. Pancreatic NETs (PNETs), previously known as islet cell carcinomas, arise from pancreatic ductal progenitors. Extrapancreatic low- to intermediate-grade NETs are generally called carcinoids and most often originate along the aerodigestive tract. These tumors share the capacity for hormone production and usually have an indolent clinical course. Presenting symptoms are caused by secreted hormones, local tumor growth, and/or metastasis. Surgical resection is the curative approach for localized disease. In unresectable or metastatic disease, long-acting somatostatin analogues improve quality of life and progression-free survival. In PNETs, recent randomized studies support the use of targeted therapies such as everolimus and sunitinib, with older prospective and retrospective data supporting the use of alkylating chemotherapy such as streptozocin and temozolomide. This chapter presents a comprehensive overview of the diagnosis and management of pancreatic and extrapancreatic NETs.
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The overall incidence of NETs in the United States is rising and presently estimated at 5.25 cases per 100,000 (1). Most NETs progress slowly and may remain undiagnosed for years or even a person’s entire natural life. Small bowel NETs are found in 0.65% to 1.2% of patients during unselected necropsy (2,3). These tumors are usually diagnosed in the sixth and seventh decades of life (1,4). The gastrointestinal tract is the most common primary site of NETs, accounting for 58% of NETs (1). The distribution of NETs is illustrated in Table 26-1.
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The prognosis for patients with NETs varies by histologic grade, stage, and primary site. High-grade NETs demonstrate similar biology and prognosis to small cell lung carcinoma. Low- to intermediate-grade NETs have a more favorable prognosis. The median overall survival of patients with localized low- to intermediate-grade NET is 223 months, according to a recent analysis of the Surveillance, Epidemiology, and End Results (SEER) database of patients registered from 1973 to 2004. For patients with regional disease, defined as involvement of regional lymph nodes, extension to adjacent tissue, or both, the median overall survival is 111 months. For metastatic disease, the median overall survival is 33 months (1). The prognoses ...