Pathology of fore and midgut neuroendocrine tumours

There is much confusion in both definition and practical issues among pathologists and clinicians alike for neuroendocrine tumours/carcinomas (NETs/NECs). This review focuses the attention on key issues of foregut and midgut NET: pathological features (nomenclature, classification, diagnostic criteria, grading, staging, markers and prognosis), molecular genetics, and how to approach common problems in NET (multifocal vs multicentric, metastatic potential and prediction of primary site). The value of the term neuroendocrine is related to its connotation of a particular phenotype or differentiation pattern. Accordingly, the NET nomenclature can be addressed by using any of the following groups of terms: (1) well-differentiated NET, well-differentiated NEC, or poorly differentiated NEC; or (2) NECs (grades IeIII), indicating in an explanatory note the equivalent terminology, when appropriate. Ultimately, the use of specific NET terms remains a personal preference, but what is the most critical is the necessity that the terms will be understood by health professionals caring for patients and that the terms can be grouped and translated for epidemiologic and molecular studies that can offer unique targets for specific therapies.