Changes in categorization or nomenclature within Neuroendocrine Tumours.

The 5th Edition of WHO classification of neuroendocrine neoplasms is built to achieve a uniform terminology and to define a similar diagnostic scheme across different anatomical locations. At variance with the 4th edition, a chapter discussing neuroendocrine neoplasms in non-neuroendocrine organs has been introduced, that proposes a binary system for classification segregating well differentiated neoplasms, termed neuroendocrine tumors (NET), and poorly differentiated neoplasms, termed neuroendocrine carcinomas (NEC). A grading system for NET is based on mitotic index and/or Ki-67 index and/or necrosis, depending on the different location. If already well-established in the digestive system, this approach modifies and homogenize the classification of neuroendocrine neoplasms in the urinary tract, in female genital organs and in the male genital system. In the lung and thymus, the double terminology of carcinoid/NET, already introduced in the 5th Edition of the WHO classification of thoracic tumors, is endorsed. This approach undoubtedly helps the multidisciplinary approach for the diagnosis and clinical management of patients affected by these neoplasms, without losing site-specific characteristics that influence the clinical and biological behavior of tumors in different anatomical sites. Other major advances of the new WHO scheme are the homogenization of epidemiological data and the correct integration of data from prospective future studies aimed at the definition of molecular profiles and at the identification of tumor type-specific and patient-specific therapeutic approaches.