CYTOGENETIC ASPECTS OF PEDIATRIC GERM-CELL TUMORS

We have performed in situ hybridization (ISH) studies predominantly on paraffin sections and on isolated nuclei of 22 pediatric germ cell tumors (GCTs) from 18 patients including 4 recurrences from three patients. In addition, we performed conventional cytogenetic analyses in three tumor samples. Because reports on cytogenetic studies in pediatric GCTs are scarce we focused our studies on those chromosome abnormalities frequently observed in adult GCTs. These included numeric and structural abnormalities of chromosomes 1 and 12 (e.g. isochromosome 12p) and numeric deviations of chromosomes 8, 10, X and Y. The histological subsets of the tumors investigated included two dysgerminomas (DGE), one seminoma (SE), one combined seminoma, two embryonal carcinomas (EC), two recurrent ECs, six pure yolk sac tumors (YST), five combined teratomas, one immature teratoma (IT) and two recurrences of IT, and three differentiated teratomas (TD). Similar to the GCTs in adults, additional copies of chromosome 12 were the most frequently observed numeric abnormalities. The analysis of two paraffin-embedded tumors suggested that changes in the size of the pericentromeric hybridization signals of chromosome 12 may be attributed to the presence of i(12)(p10). This was confirmed following the karyotype analysis of one EC which unequivocally revealed the presence of two i(12)(p10). Interestingly, using these probes, no chromosomal abnormalities were found in the pure TD or in the TD cells of mixed tumors containing a YST component. In the YST portion, however, the 1p deletions and/or numeric chromosome changes were present. Surprisingly, deletions at the short arm of chromosome 1, del(1)(p36.3), were frequently observed in malignant pediatric GCTs and were the sole abnormality detected in one case. The 1p36 deletions were present not only in all stage IV ECs and YSTs investigated, but occurred also in some stage I YSTs and were always absent in the relatively benign TDs. Our results indicate that deletions at 1p36 play a role in the differentiation capacity and may serve as a prognostic marker in pediatric GCTs.