Chromosomal gains and losses in testicular germ cell tumors of adolescents and adults investigated by a modified comparative genomic hybridization approach.

Testicular germ cell tumors of adolescents and adults, both seminomas (SE) and nonseminomas (NS), are aneuploid, and classical karyotyping demonstrated a specific pattern of gains and losses. More recently, these data have been supported by in situ hybridization and comparative genomic hybridization (CGH) on a limited number of samples. Interpretation of CGH results is complicated by the intermediate ploidy of these tumors (3-4 n for SE and 2-3 n for NS). To circumvent this problem, this particular study was undertaken. CGH was performed on 8 SE and 10 NS, after which two single chromosome normalizations were applied, one for chromosome 4 (found to be associated to the lower ploidy level of the tumor) and one for chromosome 8 (found to be associated with the higher ploidy level of the tumor) Using this modified CGH interpretation method, chromosomal regions with a similar copy number of chromosome 4 and 8 were identified as belonging to the lower and higher ploidy level, and the regions below chromosome 4 and above chromosome 8 were identified as lost or gained outside the ploidy range of the tumor, respectively. Our results are in accordance with earlier findings, however they add novel data, including comparison of SE and NS. This approach reveals relevant information about the chromosomal constitution of testicular germ cell tumors, leading to a better understanding of the pathogenesis of these tumors.

Chromosomal constitution of human spermatocytic seminomas: comparative genomic hybridization supported by conventional and interphase cytogenetics.

No data on the chromosomal constitution of spermatocytic seminomas are available thus far because of their rarity. Ploidy analysis performed on paraffin-embedded cases showed varying results from (near-) diploid to aneuploid. We applied comparative genomic hybridization on four snap-frozen primary spermatocytic seminomas of three different patients. Conventional cytogenetic analysis was successful in one, and "interphase cytogenetics" with centromeric region-specific probes was applied to another. The results from comparative genomic hybridization showed almost exclusively numerical chromosomal aberrations, in agreement with the data from karyotyping. Despite the limited number of cases studied, a nonrandom pattern of chromosome imbalances was detected: chromosome 9 was gained in all spermatocytic seminomas. This suggests that that this aberration plays a role in the development of this cancer. Interphase cytogenetics shows that the copy number of most chromosomes ranges from two to four, with an average of near trisomic. This constitutes the first report on the chromosomal constitution of spermatocytic seminomas.

Comparative genomic hybridization in hypotriploid/hyperdiploid tumors.

Hypotriploidy/hyperdiploidy ("intermediate ploidy") often occurs in testicular germ cell tumors of adolescents and adults. Disomic and trisomic chromosomes represent significant parts of the tumor genome and a few chromosomes fall outside the two- to three-copy number range. We performed comparative genomic hybridization (CGH) with DNA isolated from a cell line from a case of testicular germ cell tumor of adolescents and adults and found most of the ratio values to be dislocated from the baseline 1.0 and placed adjacent of the diagnostic thresholds of 0.8 and 1.2. We attributed that to the fact that, in current software packages for analysis of CGH, the fluorescence ratio baseline is assumed to correspond to the copy number of most loci of the genome. We then evaluated, instead of the commonly used fluorescent ratio value from the whole metaphase, the use of the fluorescence ratios of single chromosomes. The results permitted a clear distinction between the chromosomes with two and three copies and, in particular, of the regions deleted or amplified outside the two- to three-copy range. We concluded that the evaluation of unbalances of DNA copy number in intermediate ploidy cases is best carried out using multiple normalization.