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Comparative genomic hybridization (CGH) is a molecular-cytogenetic method for the analysis of copy number changes( gains /losses) in the DNA content of tumor cells. The method is based on the hybridization of fluorescently labeled tumor ( fluorescein) and normal DNA ( texas red) to normal human metaphase preparations. Using epiflourescence microscopy and quantitative image analysis, regional differences in the fluorescence ratio of tumor vs. control DNA can be detected and used for identifying abnormal regions in the tumor cell genome. CGH will detect only unbalanced chromosomes changes. Structural chromosome aberrations such as balanced reciprocal translocations, inversions can not be detected.

DNA from tumor tissue and from normal control tissue (reference) is labeled with different colors. After mixing tumor and reference DNA along with unlabeled human cot 1 DNA to suppress repetitive DNA sequences, the mix is hybridized to normal metaphase chromosomes or, for array- or matrix-CGH, to a slide containing hundreds or thousands of defined DNA probes. The (fluorescence) color ratio along the chromosomes is used to evaluate regions of DNA gain or loss in the tumor sample.

See also : Oncogene -- Tumor suppressor gene -- Carcinoma -- Sarcoma -- Lymphoma -- Leukemia