An extragonadal yolk sac tumor presumed to be of postmeiotic germ cell origin by genetic zygosity analysis via single nucleotide polymorphism array.

An extragonadal yolk sac tumor (YST) is a rare malignant germ cell tumor that usually occurs in childhood. The pathogenesis of extragonadal YST remains largely unknown, especially with regards to its cell of origin. Herein, we report a case of extragonadal YST arising in the uterine round ligament. A 31-year-old Japanese woman, para 2, underwent partial resection of a left-sided, 5-cm, solid inguinal mass. Intraoperative findings showed enlargement of the uterine round ligament in the inguinal canal. Pathological evaluation diagnosed the mass as YST with a mature teratoma (MT) component. The preoperative α-fetoprotein level was markedly elevated, at 24 790 ng/mL. Postoperative magnetic resonance imaging revealed a right ovarian MT and a 3-cm mass remaining in the left lower abdominal wall. The patient underwent total abdominal hysterectomy, bilateral adnexectomy, and left inguinal mass resection. We sampled three frozen tissues (YST, right ovarian MT, and left normal ovary) and performed a single nucleotide polymorphism (SNP) array. Pathological evaluation revealed remnant extragonadal YST in the left inguinal region. The SNP array demonstrated a completely homozygous YST genotype. Copy number variations were gains of 1p, 1q, 2p, 3p, 7p, 8p, 10q, 14q, 18p, 20q, Xp, and Xq and losses of 12q, 20p, and Xq. The right ovarian MT and left normal ovary were partially homozygous and heterozygous, respectively. The evidence suggests that this neoplasm is presumed to be a postmeiotic germ cell origin.