Fluorescent In Situ Hybridization(FISH) is a method used to determine cell ploidy and locate a target segment of DNA on a chromosome. The DNA of interest is labeled with a fluorescent dye and hybridized to a cytological preparation of chromosomes that has been denatured to allow nucleic acid hybridization between chromosomal DNA and the probe. The site of hybridization is determined by fluorescent microscopy. Generally, FISH is a hybrid of 3 technologies: cytogenetics, fluorescence microscopy, and DNA hybridization.
FISH labels probes nonradioactively with fluorochromes, or biotin and fluorochrome-labeled avidin, with digoxeginin and fluorochrome-labeled anti-digoxeginin, or others; the use of multiple band-pass filters allows simultaneous viewing of numerous probes for different chromosomal sequences labeled with different fluorochromes. FISH is very useful in cytogenetic studies, where probes for particular chromosomes or chromosomal regions can be used for the prenatal diagnosis of common aneuploidies or to detect early stages of lymphoproliferative disorders and is as sensitive as other analytical techniques.
In genetics, FISH provides a physical mapping approach to detect hybridization of probes with metaphase chromosomes and with the less-condensed somatic interphase chromatin. It is a test that maps the genetic material in a person’s cells. This test can be used to visualize specific genes or portions of genes. FISH testing is done on breast cancer tissue removed during biopsy to see if the cells have extra copies of the HER2 gene. The more copies of the HER2 gene that are present, the more HER2 receptors the cells have. These HER2 receptors receive signals that stimulate the growth of breast cancer cells.The results will tell people that the cancer is either positive or negative. Generally, the FISH test is not as widely available as another method of HER2 testing, called ImmunoHistoChemistry, or IHC. However, FISH is considered more accurate. In many cases, a lab will do the IHC test first, ordering FISH only if the IHC results don’t clearly show whether the cells are HER2-positive or negative.
In FISH, fluoresceinated chromosome probes are used for cytologic analysis and cytogenetic studies, and to detect intratumoral heterogeneity. FISH probes are designed for rapid identification of a wide range of chromosomal aberrations across the genome. Fish probes can be used for diagnosing syndrome or diseases, with accuracy of 95%. Creative Bioarray’s CABRTM probes target relevant regions for a wide range of applications such as detection of gene amplification, deletion, translocation and chromosomal aneuploidies associated with tumor and genetic disease profiling; this makes molecular diagnostic technology important for clinical diagnosis and pharmaceutical industry.