Fluorescence in situ hybridization (FISH) in cytogenetics of leukemia

The principle of the fluorescence in situ hybridization (FISH) method is in the base pairing of the DNA probe to complementary sequences in the studied specimen. The hybridization of specific DNA or RNA probes to the cellular targets attached to the microscopic slides is widely used for the identification of chromosomal translocations, deletions, amplifications of specific genes, and chromosome number changes in mitotic and/or interphase cells. The use of FISH with the modifications of the basic method meant a breakthrough in detection and diagnosis of human malignancies. During the last tow years FISH was used in our laboratory for: (a) identification of constitutive and acquired numerical and structural chromosomal abnormalities; (b) detection of minimal residual disease or early relapse in patients treated for leukemia by bone marrow transplantation (BMT) and/or chemotherapy; (c) determination of the cytogenetic pattern of non-dividing or terminally differentiated cells. To confirm the structural rearrangements found by the classical G-banding technique, the whole chromosome painting probes which hybridize to multiple chromosomal sequences were used. The alpha-satellite DNA probes which detect centromeric repetitive sequences were utilized for determining the numerical and sex chromosome changes. Specific unique chromosomal sequences which can confirm all chromosomal rearrangements, i.e., deletions, translocations or inversions with the corresponding breakpoints were introduced for specific cases. Recently, every chromosomal translocation, deletion and any other structural or numerical change found by conventional cytogenetic analysis in the bone marrow cells of the patients with leukemia has been verified in our laboratory by FISH. The results of this study showed that FISH is more efficient than conventional cytogenetics in detecting residual malignant cells. For chromosomal rearrangements FISH is an extremely sensitive method which not only verifies but also interprets with more precision the findings of classical cytogenetics.