Pavlidis N, et al. - Using the Surveillance, Epidemiology and End Results registry, 1990–2015, researchers evaluated incidence rates, modeled relative risks and survival of adolescents and young adults (AYA) patients with cancer of unknown primary (CUP). The definition of standard pathology classifications was met by 907 of 2,480 AYA patients. In most of the cases of CUP in AYA, a neuroendocrine, squamous cell and poorly differentiated carcinomas, with 0.4 cases per 1,000,000 population, were reported. The highest risks of CUP were reported among AYA residing in regions with the highest socioeconomic status level. Lower risk of CUP was seen among AYA dwelling in nonmetropolitan regions. Since the early 1990s, a slower decline has been reported with regard to the incidence of differentiated neoplasms vs that of undifferentiated neoplasms. A median overall survival (OS) of 11 months was reported, with squamous CUP showing the longest median OS 16 years.