Cell-to-cell variation of chromosomal number in the adult testicular germ cell tumors: a comparison of chromosomal instability among histological components and its putative role in tumor progression.

By allelotyping analysis, we previously reported a putative progression pathway from germ cell neoplasia in situ (GCNIS) to seminoma, then to embryonal carcinoma in mixed-type testicular germ cell tumors (TGCTs), and detected that loss of heterozygosity events in seminoma components in mixed tumors were more frequent than those in pure seminomas. To elucidate a role of chromosomal instability in the progression of non-seminomatous germ cell tumor (NSGCT), we performed fluorescence in situ hybridization with centromeric probes for chromosomes 1, 7, 8, 12, 17, and X on a cohort of 52 TGCT cases with 103 histologically distinct components: 39 GCNIS lesions (16 and 23 in tumors with and without NSGCT components, respectively), 39 seminomas (27 as pure seminomas and 12 in mixed tumors), and 25 embryonal carcinomas. On a total component basis, both the mean copy number per tumor cell nucleus and the deviations from the modal number of all chromosomes examined significantly increased from GCNIS to seminoma, then to embryonal carcinoma with few exceptions. Seminoma components in mixed tumors showed a significantly greater extent of chromosomal instability in chromosomes 8 and 12 than pure seminomas, whereas no statistically significant difference was observed between GCNIS lesions with and without NSGCT components. These results suggest that not only aneuploidy, but also the cell-to-cell variation of chromosomal number is a sensitive indicator of chromosomal instability and would be implicated in the progression of NSGCT.