Abstract Chromosome banding analysis of solid tumors often yields incomplete karyotypes because of the com- plex rearrangements encountered. The addition of fluores- cence in situ hybridization (FISH) methods has helped improve the accuracy of solid tumor cytogenetics, but the absence of screening qualities from standard FISH ap- proaches has proved a severe limitation. We describe the cytogenetic analysis of ten solid tumors using G-banding followed by cross-species color banding (RxFISH), a FISH- based screening technique giving a chromosome-specific banding pattern based on the genomic homologies between humans and gibbons. The addition of RxFISH analysis in all cases led to the identification of previously unidenti- fied intra- as well as interchromosomal rearrangements, thus giving a much more certain and detailed karyotype. In two gastric stromal sarcomas, a tumor type for which no cytogenetic data were hitherto available, numerical chro- mosomal aberrations dominated, but one of the tumors also carried an unbalanced 7;17-translocation with the same breakpoint in chromosome 17 as that seen in endometrial stromal sarcomas. Introduction At the cytogenetic resolution level, the acquired genetic aberrations of hematologic malignancies have been far better characterized than those of the more common solid tumors, the latter making up only 29% of the total data base (Mitelman 1998). The reasons for this discrepancy are manifold, but both the technical difficulty of culturing tumor parenchyma cells and the cytogenetic difficulty of identifying their often complex chromosomal rearrange- ments undoubtedly play a major role. The introduction of fluorescence in situ hybridization (FISH) techniques signified an important step towards the solution of at least the second problem. Whereas the origi- nal FISH approaches were unable to cover the entire ge- nome in a single experiment and, hence, were of limited screening value, the more recent comparative genomic hybridization (CGH) and combinatorial multifluor FISH provide an unbiased, genome-wide view of all chromo- somal aberrations present in the neoplastic cells. How- ever, even these molecular cytogenetic techniques have principal limitations, in addition to whatever practical problems their use is associated with in solid tumor cyto- genetics. CGH, in which differentially labeled tumor DNA and normal DNA compete for hybridization to normal metaphase plates (Kallioniemi et al. 1992; Du Manoir et al. 1993), detects quantitatively major copy-number changes but cannot reveal balanced chromosomal rearrangements. In addition, cell-to-cell intratumor karyotypic hetero- geneity, a characteristic feature of many carcinomas (Gorunova et al. 1995; Heim et al. 1997), cannot be de- tected by this approach. Combinatorial multicolor FISH, i.e., spectral karyotyping and multiplex FISH (Schröck et al. 1996; Speicher et al. 1996), uses a pool of painting probes, each labeled with a different combination of five fluorochromes, to classify all 24 human chromosomes with distinct colors. This is excellent for the discovery of the chromosomal origin of unidentified markers in tumor karyotypes, but intrachromosomal rearrangements such as inversions and small deletions and duplications remain undetected. Cross-species color banding is a new FISH technique utilizing probes from flow-sorted, differentially labeled gibbon chromosomes (Wienberg et al. 1990; Wienberg and Stanyon 1995; Müller et al. 1997 a, b, 1998). Because Francesca Micci · Manuel R. Teixeira · Claudia U. Dietrich · Gunnar Sæter · Bodil Bjerkehagen · Sverre Heim Combined RxFISH/G-banding allows refined karyotyping of solid tumors Hum Genet (1999) 104 : 370–375 © Springer-Verlag 1999 Received: 15 January 1999 / Accepted: 5 March 1999 ORIGINAL INVESTIGATION F. Micci · C. U. Dietrich · B. Bjerkehagen · S. Heim Department of Pathology, The Norwegian Radium Hospital and Institute for Cancer Research, N-0310 Oslo, Norway G. Sæter Department of Oncology, The Norwegian Radium Hospital and Institute for Cancer Research, N-0310 Oslo, Norway M. R. Teixeira · S. Heim () Department of Genetics, The Norwegian Radium Hospital and Institute for Cancer Research, N-0310 Oslo, Norway e-mail: sverre.heim@labmed.uio.no, Tel.: +47-2293470, Fax: +47-22934440