CD10 is frequently expressed in classical seminomas.
ABSTRACT CD10 is a cell surface metalloproteinase widely expressed in various normal tissue and in epithelial, stromal or both components of various malignancies. The aim of our study was to investigate, for the first time, the expression of CD10 in a series of 135 cases of testicular germ cell tumours in order to asses its possible diagnostic and biologic significance. The expression of CD10 was studied, using immunohistochemistry, in 96 pure forms and 39 mixed forms of germinal cell tumours of the testis . Immunostaining for CD10 was positive in 68/74 (92%) seminomas and 16/24 (67%) seminomatous component of mixed germ cell tumours. The intratubular germ cell neoplasia of the unclassified type always expressed CD10. Anaplastic seminomas, embryonal carcinomas, teratoma and spermatocytic seminomas were negative for CD10. Our findings indicate that only seminomas and intratubular germ cell neoplasia, the precursors of germ cell tumours, express CD10, but when they differentiate along embryonal, somatic, trophoblastic, yolk sac lines they lose CD10 expression. CD10 could be considered a useful marker to differentiate seminoma from other forms of testicular germ cell tumours and for a better estimation of the seminomatous component in mixed germ cell tumours.