Combined RxFISH/G-banding allows refined karyotyping of solid tumors

Chromosome banding analysis of solid tumors often yields incomplete karyoty pes because of the complex rearrangements encountered. The addition of fluo rescence in situ hybridization (FISH) methods has helped improve the accura cy of solid tumor cytogenetics, but the absence of screening qualities from standard FISH approaches has proved a severe limitation. We describe the c ytogenetic analysis of ten solid tumors using G-banding followed by cross-s pecies color banding (RxFISH), a FISH-based screening technique giving a ch romosome-specific banding pattern based on the genomic homologies between h umans and gibbons. The addition of RxFISH analysis in all cases led to the identification of previously unidentified intra- as well as interchromosoma l rearrangements, thus giving a much more certain and detailed karyotype. I n two gastric stromal sarcomas, a tumor type for which no cytogenetic data were hitherto available, numerical chromosomal aberrations dominated, but o ne of the tumors also carried an unbalanced 7;17-translocation with the sam e breakpoint in chromosome 17 as that seen in endometrial stromal sarcomas.