Except for spermatocytic seminoma in adults and teratomas and yolk sac tumor in pediatric patients.
Characterized by proliferation of uncommitted neoplastic germ cells within seminiferous tubules. (Equivalent to "carcinoma in situ" in epithelial malignancies)
Present in >80% ipsilateral testis and up to 8% contralateral testis to GCT.
May also be seen in cryptorchid testis.
Basilar proliferation of atypical large cells with clear cytoplasm with centrally located large nuclei with prominent 1-2 nucleoli. (Resembles seminoma cells)
Seminiferous tubules may have decreased or absent spermatogenesis, atrophic or has thickened basement membrane.
Cells may spread in a pagetoid fashion (creeping individually within normal epithelium) to involve the rete testis.
The tumor cells may fill and distend the tubules (seminoma in situ).
Immunohistochemistry: placental alkaline phosphatase (PLAP)+, CD117+ and Oct3/4+ (like seminoma).
Progress to GCT in ~50% of cases within 5 years.