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Site, age, and gender distribution of extra-gonadal germ cell tumors in the US from 1973 to 2015.

e16051 Background: Germ cell tumors (GCT) commonly arise in post pubertal gonads where they are influenced by sexually dimorphic hormone signaling. More rarely, extra-gonadal GCTs (EGGCTs) arise in midline sites, coinciding with the route of primordial germ cell migration. EGGCTs are proposed to arise from cells not completing this migration. We characterized the incidence of EGGCTs according to patient and tumor features in an attempt to elucidate tumor origins. Methods: In Surveillance, Epidemiology, and End Results (SEER) Program SEER*Stat Database SEER 9 Regs Research Data, 1973-2015, primary EGGCT cases were identified by ICD-O-3 histologic types (seminoma: 9060-9062, 9064; non-seminoma 9065-9101) grouped into central nervous system (CNS), mediastinum, and other EGGCT sites. Age-specific incidences for males and females were divided into adolescents and young adults (AYA) defined by the National Cancer Institute as 15-39 years of age, and younger childhood and older adult groups. Results: In AYAs and older adults, age-adjusted incidence of males exceeded that of females at all sites (p≤0.006, all comparisons) (Table). Male incidence was highest in AYAs (all EGGCT, 4.35/1,000,000 person-years (Mpy); mediastinum, 2.17/Mpy; other 0.68/Mpy). Female incidence was highest in childhood (CNS, 0.86/Mpy; mediastinum, 0.14/Mpy; other 0.64/Mp-y). Conclusions: Patterns of EGGCT incidence differ substantially between sexes. Permissive extra-gonadal sites of males or male-predominant exposures may explain higher incidence in males. Alternatively, EGGCT precursor cells may have sex-specific features affecting malignant potential. [Table: see text]