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.