Of particular interest in this case is the tumor’s genetic profile: the identification of pathogenic/likely pathogenic mutations in CTNNB1 (β-catenin), ARID1A, and PIK3CA strongly supports a diagnosis of endometrioid adenocarcinoma with somatic YST differentiation rather than a primary germ cell yolk sac tumor because CTNNB1 and PIK3CA mutations are endometrioid carcinoma-specific mutations [11,12]. The gene discussed is CTNNB1; the disease is endometrioid adenocarcinoma.