Pathology reporting of neuroendocrine tumors: essential elements for accurate diagnosis, classification, and staging

Much recent debate has focused on the optimal classification of epithelial neuroendocrine tumors (NETs). Multiple different systems of terminology, grading, and staging have been proposed, and some systems combine elements of grade and stage into a single prognostic classification. Recently, national and international consensus groups have attempted to standardize the classification of NETs, especially for those arising in the gastrointestinal tract and pancreas. Furthermore, the recognition that common classification criteria (such as proliferative rate) span multiple different systems allows the basic data necessary to predict outcome and tailor therapy to be included in pathology reports, even though a single uniform system of terminology may remain elusive. Formal tumor-node-metastasis (TNM)-based staging systems also have been developed recently, and advances in the treatment of some NETs (pancreatic in particular) are pointing towards the need to assess therapeutic biomarkers in routine practice. This review will present the most widely used systems for classifying, grading, and staging NETs and will summarize the recommendations for the data to be included in standard pathology reports of these uncommon tumors.