Ki-A10, a germ cell nuclear antigen retained in a subset of germ cell-derived tumors

Monoclonal antibody Ki-A10 recognizes a nuclear antigen of 25 and 22 kd app arent molecular mass, which is abundantly expressed by immature gonocytes, spermatogonia, and spermatocytes, whereas it is absent in spermatids, sperm atozoa, oocytes, and normal somatic tissues. In a broad spectrum of human c ancers the antibody showed no reactivity except for a small subset of malig nant lymphomas, Because of this restricted expression pattern, we examined 173 germ cell tumors and 18 sex cord stromal tumors immunohistochemically t o assess the distribution of the Ki-A10 antigen. A strongly positive reacti on was found in classic seminomas, dysgerminomas, spermatocytic seminomas, and the germ cell component of gonadoblastomas. Yolk sac tumors presented a heterogeneous reactivity pattern ranging from overall positivity to comple te lack of antigen expression, and in three of eight choriocarcinomas, a fe w clusters of cytotrophoblast cells were strongly labeled. All other tumors , including Leydig and Sertoli cell tumors as well as placental tissue, wer e negative. Our findings suggest that specific germ cell antigens can be re tained in germ cell tumors along particular differentiation pathways. Ki-A1 0 is the first marker that consistently labels spermatocytic seminoma, furt her confirming its germ cell origin and suggesting a close relationship to classic seminoma, The antibody may serve for diagnostic purposes and promis es new insights into the process of germ cell differentiation and the devel opment of germ cell-derived neoplasia.