Cytogenetic investigation of testicular carcinoma in situ and early seminoma by high-resolution comparative genomic hybridization analysis of subpopulations flow sorted according to DNA content

Interpretation of data from comparative genomic hybridization (CGH) analysis of testicular neoplasms located within normal parenchyma is complicated, because the results may be influenced by a heterogeneity of subpopulations with different chromosomal aberrations and ploidy. In this study, therefore, early stages of testicular germ cell neoplasia were cytogenetically analyzed after flow sorting of nuclei according to their DNA ploidy. DNA from subpopulations with different ploidy was globally amplified by means of degenerate oligonucleotide primed polymerase chain reaction, labeled with FITC-dCTP and -dUTP by nick translation, and analyzed with high resolution CGH. A characteristic pattern of chromosomal abnormalities associated with testicular germ cell cancer (gains in 1q, 7, 8, 12, 14, 21, X; losses from 4, 5, 9, 11, 13, 18, Y) was observed in the tri- to hexaploid but not in the hyperdiploid or in pure tetraploid subpopulations. Our data suggest that subpopulations with a triploid to hexaploid DNA content purified from testes with germ cell neoplasia harbor a mixture of overt tumor and carcinoma-in-situ cells (CIS) and DNA content of CIS cells being in the triploid to hypotetraploid range, supporting the current theory of polyploidization as one of the first events of malignant transformation.