Modern view on the classification of neuroendocrine neoplasms of stomach

Neuroendocrine neoplasms (NEN) of the stomach include a heterogeneous group of neoplasms characterized by different pathogenetic mechanisms, metastatic potential, and prognosis. The incidence of gastric NAN has increased 15-fold over the past few decades. It is necessary to clearly distinguish between well-differentiated neuroendocrine neoplasms (NETs) of the stomach and neuroendocrine cancer (NECs) of the stomach, as well as mixed neuroendocrine-non-neuroendocrine neoplasms.To date, there are three classifications that are used in clinical practice: clinicopathological classification, WHO classification, and UICC TNM classification. It should be noted that over the past five years, these classifications have undergone important changes. In the clinicopathological classification, in addition to the existing three types, a number of authors proposed to add the 4th type (developing as a result of inadequate functioning of the proton pump) and the 5th type (developing in patients who receive long-term therapy with proton pump inhibitors). In the 2019 WHO classification, an important change is the acceptance that well-differentiated NETs can have a high degree of malignancy – Grade III. The main changes in the 8th edition of the TNM classification concerned the differentiation of the M symbol.Thus, to date, the classification of gastric NENs allows us to accurately characterize tumor staging, the pathogenesis underlying their development, and prognosis. They form the basis for choosing an adequate treatment strategy that makes possible to achieve the most favourable result.