Management of Neuroendocrine Tumors: Current and Future Therapies

Kjell E Öberg

Disclosures

Expert Rev Endocrinol Metab. 2011;6(1):49-62. 

In This Article

Classification

Neuroendocrine tumors have been variously described in the literature, primarily due to their diversity and complexity. They were first described in 1867 and identified as carcinomas in 1888. Siegfried Oberndorfer termed them 'carcinoid' (i.e., cancer like) in 1907,[18] but later amended this description when he recognized the potential for NETs to become malignant or metastasize. Based on embryological origin, NETs were classified in 1963 as foregut (thymus, esophagus, lung, stomach, duodenum and pancreas), midgut (appendix, ileum, cecum and ascending colon) and hindgut (distal large bowel and rectum) tumors.[19] However, this system is now considered outdated as it does not distinguish biologically relevant differences in tumors. Current best practice is to describe NETs according to their location of primary origin (e.g., pancreas and duodenum) and include reference to the resultant hormone secretion or symptoms (e.g., gastrinoma and insulinoma).

The first WHO classification of NETs was published in 1980 and applied the term 'carcinoid' to most tumors. In order to standardize terminology this was updated in 2000 and 2004 based on tumor histopathology, eliminating the term 'carcinoid tumor' (Table 2).[20] Patient prognosis is dependent upon the biological behavior of the tumor and its histological differentiation. Complementary tumor–node–metastasis (TNM) classification guidelines for the staging and grading of NETs were published by the European NETs Society (ENETS) in 2006 and 2007 (Table 3).[21,22] The ENETs TNM system is based on the WHO system and assists with the further stratification, treatment and follow-up of patients. ENETS also proposed three tumor grades based on mitotic count and proliferative index (Ki-67). Most recently (November 2009), the International Union Against Cancer/American Joint Committee on Cancer published a new TNM classification system, which is somewhat different to the ENETS system.[101]

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