Ploidy of primary germ cell tumors of the testis. Pathogenetic and clinical relevance.

The ploidy of testicular germ cell tumors (GCT), a heterogeneous group of neoplasms, was studied by DNA flow cytometry. The DNA index for infantile yolk sac tumor (N = 10), seminomas (N = 20), and nonseminomas (N = 36), was: 1.91, 1.66, and 1.43, respectively. These values differed significantly one from another (p less than 0.01). The seminoma and nonseminoma components of combined tumors (N = 16) had a significantly different median DNA index of 1.61 and 1.40, respectively. Three of the 10 infantile yolk sac tumors, but only one of the 72 testicular GCT of adults were diploid. The consistent aneuploidy of testicular GCTs of adults might be helpful in the differential diagnosis of primary nongerm cell tumors of the testis, and in differentiating between metastases of testicular GCTs and primary extragonadal malignant GCTs. These data fit into a model of pathogenesis of testicular GCTs of adults in which all tumors, with the possible exception of spermatocytic seminoma, pass through a seminoma stage. Tumor evolution seems to result from net loss of chromosomes from a (near)tetraploid carcinoma in situ cell. The pathogenesis of infantile yolk sac tumor might be different from that of testicular GCTs of adults.