American Urological Association - Yolk Sac Tumor (YST)
Yolk Sac Tumor (YST)
- Most common testicular tumor in infants and young children.
- 2 age peaks:16-18 months (Pure YST) and 25-35 years old (YST in mixed GCT).
- Pure YST in pediatric patients is not associated with ITGCN or cryptorchidism; extremely rare in adults.
- >95% of YST patients have elavated serum AFP level (100's-1000's ng/ml).
- Gross: gray white tumors with myxoid or gelatinous cut surface; +/- hemorrhage in adults because it is usually part of a mixed GCT (image A).
- Histology: multiple or variable growth patterns (12 patterns):
- Most common are microcystic, solid and myxomatous.
- Microcystic or reticular most frequent (80%) – multiple intercellular holes imparting a "sieve-like" pattern (image B).
- Other uncommon patterns include endodermal sinus, papillary, polyvesicular vitelline (vesicles lined by flattened and cuboidal cells), glandular, parietal, enteric, hepatoid, spindle and mixed patterns.
- Relatively uniform cells with clear or vacuolated to lightly eosinophilic cytoplasm.
- Endodermal sinus pattern composed of Schiller-Duval bodies, which resembles primitive glomeruli (Central vessel encircled by tumor cells, a space, and surrounded by another layer of flat tumor cells).
- Hyaline-like globules, which contain AFP and a1-antitrypsin, can be seen (image D).
- Immunohistochemistry: AFP+ and glypican-3+.
- Childhood YST has better prognosis than adult YST.
- Mixed GCTs with or without YST are treated similarly.