Aspects regarding nomenclature, classification and pathology of neuroendocrine neoplasms of the digestive system - a review.

Neuroendocrine neoplasms (NENs) of the digestive system are composed of cells with a neuroendocrine phenotype. These tumors produce and secrete peptide hormones and biogenic amines and they are called neuroendocrine neoplasms because of the marker proteins that they share with the neural cell system. The classification and nomenclature used to designate NENs have undergone changes over the past decades due to the accumulation of evidence related to the biological characteristics and their evolution. The European Neuroendocrine Tumor Society (ENETS) proposed a classification system based on the tumor grading and staging according to their localization. The latest internationally recognized NEN classification was published by the World Health Organization (WHO) in 2010. In accordance with the 2010 WHO criteria, the determination of the NEN malignancy potential is based on grading, depending on the mitotic activity and the Ki67 proliferation index, as well as on the tumor TNM stage. It is worth emphasizing that the terms neuroendocrine tumor (NET) and neuroendocrine carcinoma (NEC), without reference to grading or differentiation, are inadequate for prognostic assessment or the therapy determination, being inappropriate in pathology reports. The functional status of the tumor is based on the clinical findings but not on the pathological data or immunohistochemically profile. Despite the inability to establish a single system of sites, these are common features to establish the basis of most systems, documentation of these features allowing for greater reliability in the pathology reporting of these neoplasms.