Cytogenetic analysis of non Hodgkin's lymphomas by ratio-painting and comparative genomic hybridization reveals unsuspected chromosomal abnormalities

Cytogenetic analysis of cancer cells has proven to be a powerful tool in un derstanding malignant evolution and in providing clinically useful markers. In recent years the advent of new fluorescence in-situ hybridization (FISH ) methods such as ratio-painting and comparative genomic hybridization (CGH ) have enabled much more accurate karyotypes of malignant cells to be detec ted. In this study, we have examined the chromosomes present in malignant c ells from a series of 6 low grade follicular centre and 2 high grade diffus e large cell non-Hodgkin's lymphomas (NHL) using conventional G-banding. In all cases chromosome abnormalities were observed, including the presence o f marker chromosomes in six cases. The NHL cells were then subjected to the FISH method of ratio-painting. This provided a more accurate understanding of the origins of derivative chromosomes and identified the origins of all of the marker chromosomes. It also revealed hitherto unsuspected abnormali ties. For example, in one case four abnormal chromosomes were demonstrated to contain material from chromosome 8, which had not been previously suspec ted from G-banding, Regions of amplification and deletion on the chromosome s were also investigated by CGH, which identified further unsuspected chrom osomal abnormalities. For example, in case L124, trisomy of chromosome 7 wa s confirmed by CGH, but an unsuspected amplification of 3(p12) was also rev ealed. These approaches demonstrate the power of FISH technology in providi ng a more precise analysis of malignant cell chromosomes, and in doing so h ave produced comprehensive karyotypes of the NHL under study.