Cytogenetic and molecular analysis of human male germ cell tumors: Chromosome 12 abnormalities and gene amplification

Abstract

We report karyotypic analysis of 24 male germ cell tumors (GCTs) with clonally abnormal karyotypes biopsied from testicular and extragonadal lesions from 20 patients belonging to the histologic categories seminoma, teratoma, embryonal carcinoma, choriocarcinoma, and endodermal sinus tumor. Chromosomes 1, 7, 9, 12, 17, 21, 22, and the X chromosome were nonrandomly gained in these tumors. Nonrandom structural changes affected most frequently chromosomes 1 and 12, the latter as i(12p) and/or del(12)(q13----q22). The i(12p) was seen in 90% of tumors which included all histologic subtypes and gonadal as well as extragonadal presentation. Our present results, along with those from published data on fresh GCT biopsies, establish that i(12p) is a highly nonrandom chromosome marker of all histologic as well as anatomic presentations of GCTs. in contrast, we found del(12)(q13----q22) exclusively in nonseminomatous GCTs (NSGCTs) and mixed GCTs (MGCTs) occurring in 44% of such lesions. Because successful cytogenetic analysis of fresh tumor specimens is not always possible, we developed a method based on DNA analysis to detect i(12p) as increased copy number of 12p. In addition to the changes affecting chromosome 12 identified above, we have detected, for the first time, cytological evidence of gene amplification in the form of homogeneously staining regions (HSRs) and double minute chromosomes (dmins) in treated as well as untreated primary extragonadal and metastatic GCTs and confirmed the presence of amplified DNA in one of these tumors at the molecular level by the in-gel renaturation method. Hybridization of DNA from cultured cells from an HSR-bearing tumor with a panel of probes for genes known to be amplified or otherwise perturbed in diverse tumor systems did not identify the amplified gene, suggesting amplification of a novel gene or genes. This study comprises the largest series of GCT cytogenetics attempted so far. Notably, it includes data on a series of primary mediastinal tumors, a group which previously has not been studied in any detail.

Fluorescence in situ hybridization-based approaches for detection of 12p overrepresentation, in particular i(12p), in cell lines of human testicular germ cell tumors of adults

“…Cytogenetically, i(l2p) can be detected in most TGCT [7,38,39], supported by molecular data [39, 4 0 ], The FISH approach [ll] is based on the use of a cen tromere specific probe for chromosome 12. This probe has been reported to detect a consistent size difference between the hybridizing region of a normal chromosome 12 and an i(12p), Because of a discrepancy in the literature regarding this phenomenon [18-20, 23, 41], as well as the occur rence of TGCT without i(12p) [1 3 , 20, 42], we studied the possibility of identifying 12p overrepresentation in gen eral, and of i(12p) in particular, on metaphase spreads and interphase nuclei with a double FISH approach.…”

Oncogenes in human testicular cancer: DNA and RNA studies

“…Cytogenetically a specific chromosome marker has been found in more than 80% of testicular germ cell tumours: an isochromosome for the short arm of chromosome 12 [i(12p)] (Castedo et al, 1988;Samaniego et al, 1990). The i(12p) copy number has been reportd to have prognostic significance (Bosl et al, 1989).…”

Germ cell tumors of the gonads: a selective review emphasizing problems in differential diagnosis, newly appreciated, and controversial issues

“…[7][8][9] DNA quantification shows that mature ovarian teratomas are diploid, and cytogenetic study demonstrates that they almost always have a normal 46,XX karyotype, 10,11 whereas mature teratomas of the postpubertal testis are hyperdiploid to hypotriploid with complex cytogenetic abnormalities including invariable 12p amplification, often in the form of an isochromosome [i (12p)]. [12][13][14][15][16] Molecular genetic analysis has also shown that mature ovarian teratomas are usually homozygous for polymorphic markers, 17 indicating that they derive most often from a germ cell that has completed meiosis I but not meiosis II, a conclusion supported by cytogenetic analysis. 11 When heterozygosity does occur, it predictably is in loci that tend to be located distant from the centromere-that is, in genes most susceptible to crossing over at the metaphase plate of meiosis I.…”