Comparative genomic hybridisation (CGH) is a new cytogenetic method, which is based on a combination of fluorescence microscopy and digital image analysis. The molecular genetic basis is the hybridization of a mixture of fluorescein labeled test-DNA and reference-DNA on normal metaphase chromosomes. Comparative analysis allows the identification of all unbalanced chromosomal aberrations of the test-DNA in a single experimental step. The resulting DNA gains or DNA losses on the chromosomal or subchromosomal level mirror possible amplifications of oncogenes or losses of suppress orgenes. As CGH can be performed with genomic DNA of formalin-fixed and fresh-frozen tissue or cells, this new method is a very effective tool for pathologists and cytologists in the extended genomic screening of tumors and genetically altered tissues. Despite CGH analysis at present is restricted to research applications; its widespread dissemination as a routine method in diagnostic pathology can be expected in the near future.
