OVERREPRESENTATION OF CHROMOSOME 12P SEQUENCES AND KARYOTYPIC EVOLUTION IN I(12P)-NEGATIVE TESTICULAR GERM-CELL TUMORS REVEALED BY FLUORESCENCE IN-SITU HYBRIDIZATION

Human testicular germ-cell tumors (TGCTs) comprise a heterogeneous gro up of solid neoplasms. These tumors are characterized by the presence of a highly specific chromosomal abnormality, i.e., an isochromosome o f the short arm of chromosome 12. At present, this i(12p) chromosome i s found in more than 80% of TGCTs. Isochromosome 12p has also been obs erved in some ovarian and extragonadal germ cell tumors. In the remain ing so-called i(12p)-negative TGCTs other abnormalities involving chro mosome 12, mainly 12p, can be found. In order to establish whether 12p abnormalities other than i(12p) are a common phenomenon in TGCTs, a p anel of 11 i(12p)-negative tumors was investigated using multicolorflu orescence in situ hybridization. All TGCTs examined appeared to contai n chromosomal abnormalities involving 12p, resulting in a distinct ove rrepresentation of short arm sequences. In addition, indications were obtained for a clonal evolution in one of the tumors. Our data suggest that the occurrence of 12p abnormalities is a common phenomenon in i( 12p)-negative TGCTs and that these abnormalities, analogous to i(12p), may contribute to the process of tumor development.