Neuroendocrine Tumors

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Carcinoid tumors are a subset of neuroendocrine tumors and overall incidence of carcinoids in the United States is estimated at 5.25 cases per 100,000 population. The majority of carcinoid tumors arise within the gastrointestinal tract (58%), with the pulmonary system as the next most common site of origin (27%). The remainder (15%) arises from other or unknown locations1.

Pulmonary neuroendocrine tumors comprise a spectrum of tumors including low grade neuroendocrine tumors (typical carcinoids), intermediate grade neuroendocrine tumors (atypical carcinoids) and high grade neuroendocrine tumors (large cell neuroendocrine and small cell carcinomas). Carcinoid tumors comprise about 0.5 to 5% of all lung tumors and are malignant tumors with the potential to metastasize.2-4 Typical carcinoids comprise about 90% of all pulmonary carcinoids and show a high degree of differentiation, rare mitoses (<3 mitotic figures/10 hpf), scarce pleomorphism or necrosis. The remaining 10% are atypical carcinoids, which are characterized by increased mitotic activity (>3 but <10 mitoses/ 10 hpf, cellular atypia and increased pleomorphism or necrosis. Atypical carcinoids tend to have a higher rate of metastasis and are larger at the time of diagnosis.4 Specimens with >10 mitoses/10 hpf are either small cell or large cell neuroendocrine carcinomas. Of these features, it has been shown that only the number of mitoses is a predictor for prognosis.5

There is no known association between typical
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