Neuroendocrine tumors (NETs): historical overview and epidemiology.

Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms which take origin from the neuroendocrine cell system and are characterized by embryological, biological and histopathological differences. Traditionally considered as a rare and "niche" pathology, over the last decades they have gained significant attention from the scientific community, even because of their increasing incidence and prevalence probably imputable to the availability of more sensitive diagnostic tools and to the development of higher awareness among clinicians. This paper retraces the key events that led to the discovery, characterization and classification of NETs as well as to the development of adequate treatment strategies. Incidence and epidemiology are also addressed.