The expression of an oncofetal
protein, the
glypican-3 (GPC3), was immunohistochemically evaluated in a wide variety of primary testicular
germ-cell tumors (GCTs) in comparison with other markers,
alpha-fetoprotein (AFP),
human chorionic gonadotropin (
hCG)-beta, and OCT3/4. Eighty-nine cases of GCT including 22 cases of mixed GCT were evaluated with reference to each
tumor component. GPC3 expression was observed in neoplastic cells of
yolk-sac tumor (YST) (25/25),
teratoma (2/10), components of syncytiotrophoblastic giant cells (STGCs) (10/14), and
choriocarcinoma (1/3), but none in intratubular germ-cell
neoplasias, unclassified type (0/33),
seminomas (0/61), or
embryonal carcinoma (0/19). All cases of YST showed diffuse labeling of neoplastic cells in cytoplasmic and membranous patterns, and the positive area of GPC3 was much larger than that of AFP. Glandular structures in
teratomas showed GPC3 immunostaining as well as AFP. Although the number of GPC3-positive cells was smaller in STGC components and
choriocarcinoma, there was no diffusion artifact in GPC3 immunostaining, as was frequently encountered in
hCG-beta staining. Thus, GPC3 is a unique oncofetal
protein, which is useful as an immunohistochemical marker for GCT differentiated to extraembryonic tissue, especially YST.