The totipotential germ cells that differentiate toward extraembryonic fetal membranes give rise to yolk sac tumours.
Yolk sac tumor is the most common testicular tumour in infants and young children.
Prognosis is good in children up to 3 years of age.
In its pure form, yolk sac tumor is rare in adults; however, it is present in 44% of adult cases of mixed germ cell tumour.
Alpha-fetoprotein is normally produced by the embryonic yolk sac, and thus serum alpha-fetoprotein levels are elevated in greater than 90% of patients with yolk sac tumour.
Grossly, pure forms present as infiltrative, homogeneous, yellow-white, mucinous lesions.
Microscopically, they are composed of cuboidal tumour cells, arranged in a lace-like (reticular) network, solid areas, multiple microcysts and papillae, all in a background of myxoid stroma. Structures resembling primitive glomeruli (Schiller-Duval bodies) , so-called endodermal sinuses, are seen in 50% of cases. These structures consist of a microcyst with a central fibrovascular core.
Immunocytochemically, eosinophilic, hyaline globules containing immunoreactive alpha-fetoprotein (AFP) and alpha-1-antitrypsin are present within and around the tumour cells.
The descriptive name endodermal sinus tumour and yolk-sac tumour reflects the histologic similarity of this tumour to the structure of the rat placenta.
If the yolk sac tumor is confined to the testis at the time of orchiectomy (as it is in over 80% of cases) and if the serum level of alpha-fetoprotein is not elevated, the patient can be closely monitored without further therapy and the prognosis is excellent. If relapse occurs, chemotherapy is the treatment of choice. The lungs are the most common site of recurrent disease.
Abstract: Hepatoid variant of yolk sac tumor of the testis. Pathol Int. 2000 Sep;50(9):754-8.
A case of testicular yolk sac tumor (endodermal sinus tumor) consisting predominantly of hepatoid cells is documented. A mass measuring approximately 4 x 3 cm was noted in the left testis of a 64-year-old man. Preoperative examination revealed an elevated serum level of alpha-fetoprotein (5479 ng/mL). Histologically, the lesion was composed predominantly of sheet-like or trabecular proliferation of hepatocyte-like cells with eosinophilic or clear cytoplasm. The tumor cells were immunoreactive for alpha-fetoprotein, antimitochondrial antibody, cytokeratin (AE1/AE3), alpha-1-antichymotrypsin, alpha-1-antitrypsin, albumin, carcinoembryonic antigen and epithelial membrane antigen. It was necessary to distinguish this variant lesion from metastatic hepatocellular carcinoma, embryonal carcinoma and hepatoid carcinoma.