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Yolk Sac Tumor (YST)

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  • 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.

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    • 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.