Rougemont AL, et al. - This investigation was performed to identify the role of HNF1β in the differential diagnosis from other germ cell tumors (GCT). For this research, a cohort of 49 yolk sac tumor (YST) specimens from 45 patients were designed, occurring either as pure tumors, or as a component of a mixed GCT. Using HNF1β, immunohistochemistry was conducted on whole tumor sections. The findings from the present study suggested that HNF1β is a sensitive and reliable marker of the YST component in GCT, and allows distinction of YST from intricately admixed embryonal carcinoma (EC), particularly in the diffuse embryoma pattern.