Analysis of chromosome 12 aneuploidy in interphase cells from human male germ cell tumors by fluorescence in situ hybridization.

The i(12p) marker chromosome has been found to be a highly nonrandom chromosome abnormality associated with germ cell tumors (GCTs). We have previously shown that a chromosome 12 centromere specific alpha-satellite DNA probe detects the i(12p) by virtue of differences in the size of the signal originating from the i(12p) and normal chromosome 12 centromeres after fluorescence in situ hybridization (FISH) in metaphase and interphase cells of cultured GCT cell lines. We have now extended this analysis to 72 fresh GCT tumor biopsy specimens. Banded cytogenetic analysis was attempted on each of these tumors, 45 of which were found to be clonally abnormal. Data on i(12p) and chromosome 12 copy number obtained by FISH agreed well with those obtained by cytogenetic analysis. In addition, the FISH method made possible the detection and determination of i(12p) and the chromosome 12 copy number in cases in which conventional cytogenetic analysis was unsuccessful. We found the incidence of i(12p) in seminomas to be low (7%) compared to that in nonseminomas (75%) when tumor biopsy specimens were studied by FISH. Our results show that the FISH technique can be used reliably for detection of the diagnostically and prognostically useful i(12p) marker in GCT tumor biopsy specimens.