Neuroendocrine tumors (NETs) originate from neuroendocrine cells located throughout the body. This chapter focuses on low- to intermediate-grade NETs, though the term "neuroendocrine tumor" also denotes diseases such as small cell carcinomas of pulmonary and extrapulmonary origin, thyroid medullar carcinoma, neuroblastoma, and Merkel cell tumor. Islet cell carcinomas, also known as pancreatic endocrine tumors, pancreatic NETs, or pancreatic carcinoid, arise from the islets of Langerhans. Low- to intermediate-grade NETs arising from other sites are generally called carcinoids and are localized most often in the gastrointestinal tract or bronchopulmonary tree. These tumors share the capacity for hormone production and usually have an indolent clinical course. Presenting symptoms, when present, are caused by excess hormones, local tumor growth, and/or metastasis. Surgical resection is the curative approach for localized disease. In unresectable and/or metastatic disease, long-acting somatostatin analogues such as octreotide have significantly improved quality of life. The roles of newer targeted agents are under investigation in phase III trials discussed in this chapter. This chapter also presents sample clinical cases from the MD Anderson Cancer Center to illustrate the challenges of caring for the NET patient and the utility of the multidisciplinary approach.
The overall incidence of NET in the United States is estimated at 5.25 cases per 100,000 (1). Most NETs progress slowly and may remain undiagnosed for many years. Of note, carcinoid tumors were found in 0.65 to 1.2% of patients during unselected small intestine necropsy (2,3). These tumors are usually diagnosed in the sixth and seventh decades of life. NETs have been described as more common among African Americans owing to a higher diagnosed incidence of rectal carcinoid (1,4). The gastrointestinal tract is the most common primary site of NETs, accounting for 58% of all carcinoid tumors (1). The distribution of NETs is illustrated in Table 23-1.
Table 23–1. Organ Distribution of Neuroendocrine Tumors (Carcinoids and Pancreatic Islet Cell Tumors) |Favorite Table|Download (.pdf)
Table 23–1. Organ Distribution of Neuroendocrine Tumors (Carcinoids and Pancreatic Islet Cell Tumors)
|Organ Site||Distribution (%)|
The overall prognosis for patients with NET varies by histologic grade, extent of disease, and site of primary tumor. High-grade NETs have high metastatic potential and an aggressive growth pattern, and the treatment strategy is similar to that for small cell carcinoma of the lungs. Most low- to intermediate-grade NETs have a more favorable prognosis than adenocarcinoma of the same primary site. The median overall survival duration 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 ...