Mixed Neuroendocrine and Non-neuroendocrine Neoplasms (Mi NEN)

Mixed neuroendocrine non-neuroendocrine neoplasms (MiNENs) is the term that the 2019 WHO classification has adopted to decline all digestive neoplasms consisting of at least 30% by a neuroendocrine and a non-neuroendocrine component. MiNENs category represents the results of a plethora of terminologies that have followed over time. At present, MiNENs category encompasses well- and poorly differentiated neuroendocrine components, differently to MANECs term that included only poorly differentiated NECs. MiNENs represent a rare category of neoplasms that account an incidence of 0.01 on 100,000 population per year. The rarity of the disease and the strict diagnostic criteria lead that MiNENs mostly be underestimated. Indeed, in diagnostic process, biopsy could not be representative of whole tumoral mass, underestimating the features of one or both the components. MiNENs virtually can arise from every tissue or organ, but 2019 WHO classification has accepted the term only for digestive NENs, even if some authors put forward the idea of an extension of the term MiNENs to the other neoplasms over GEP tract.