PATHOLOGY OF NEUROENDOCRINE TUMORS

Neuroendocrine (NE) tumors are a heterogeneous group of neoplasms aris ing in various organs and sharing the features of the NE cell system. The term ''neuroendocrine'' is used for cells characterized by their s ecretory products and some cytoplasmic proteins rather than by their l ocalization and embryological derivation. Some tumor types can show a characteristic pattern an conventional histology but, to obtain an acc urate diagnosis of many NE tumors it is necessary to employ various sp ecial methods, mainly electron microscopy and immuno-histochemistry. T he classification of NE tumors in four categories according to Travis et al. is largely used : typical carcinoid and atypical carcinoid are low grade neoplasms; small cell NE carcinoma and large cell NE carcino ma are high grade neoplasms. The size, extension into surrounding tiss ues, angioinvasion and hormonal function are also important to conside r in the prognostic evaluation of some NE tumors. Tumors exhibiting mu ltidirectional differentiation must be classified in carcinoma with in terspersed NE cells, carcinoid with interspersed non NE cells, composi te tumors and amphricine tumors. Finally, some NE rumors may present f eatures suggesting a Multiple Endocrine Neoplasia, ie. multifocality a nd association with hyperplasia of endocrine cells.