The Application of Fluorescence in situ Hybridization (FISH) in Haematological Malignancies

Abstract

The Philadelphia chromosome involves the reciprocal translocation between the long arms of chromosome 9 (9q34) and chromosome 22 (22q11.2) involving the ABL and BCR gene. This leads to the formation of two fusion genes, the BCR/ ABL fusion gene on derivative chromosome 22 (the Philadelphia chromosome) and the ABL/BCR on derivative chromosome 9. The Philadelphia chromosome is detected in 95% of cases with chronic myeloid leukemia, in 2-5% of cases in childhood ALL, 25% of cases in adult ALL and in 3% of acute myeloid leukemia. The Philadelphia chromosome is detected by cytogenetic and molecular techniques. Fluorescence in situ hybridization (FISH) is a molecular cytogenetic technique that allows the hybridization of chromosomal abnormalities by the hybridization of a fluorescent labelled DNA probe to target DNA. The main aim behind this dissertation was to optimize and apply FISH technique using the LSI BCR-ABL double fusion probe for the detection of the Philadelphia chromosome in 41 cases of haematological malignancies. The Philadelphia chromosome was detected in fifteen out of fifteen cases of CML cases and in one out of thirteen cases of acute lymphoblastic leukemia There was no evidence of Philadelphia chromosome by FISH in a117 cases of acute myeloid leukemia and in all 6 suspected CML cases that showed overlapping features with other myeloproliferative disorders. In conclusion, this study was successful in optimizing a FISH method that can be used routinely as a diagnostic and a prognostic tool for the detection of the Philadelphia chromosome in haematological malignancies. Moreover, the application of FISH was useful in complementing conventional cytogenetics to detect the Philadelphia chromosome in cases were no dividing cells were present, in cases with poor chromosome morphology, and in cases with complex rearrangements.