Fluorescence in situ hybridization (FISH) is a method of molecular cytogenetics. It is based on the hybridization (binding) of a specific single strand-DNA marked with fluorescence to the corresponding counter strand-DNA in the investigated cell. This method can be used with nuclei in metaphase with visible chromosomes (metaphase-FISH) or with nuclei in interphase, e.g. in tissue sections. With FISH, major deletions or insertions as well as translocations can be demonstrated. Point mutations and small deletions or insertions are not detectable by FISH. Since only specific DNA-probes are used, only specific questions can be answered. A screening for unknown chromosomal aberration is not possible.
FISH-analyses play an important role in diagnosis and prognosis of various hematological neoplasms such as acute myelocytic leukemia, myelodysplastic syndromes or chronic lymphocytic leukemia.