Results of Conventional Cytogenetics and Interphase FISH (I-FISH) Analyses in Patients with a Clinical and Morphologic Diagnosis of CML: Analysis of 52 Cases.

The presence of the Philadelphia chromosome (Ph), derived from a balanced translocation between chromosomes 9q and 22q, serves as a hallmark for the diagnosis of CML or Ph-positive ALL. In recent years, I-FISH has become the method of choice to detect Ph-positive clones at diagnosis and during treatment. In addition, I-FISH analysis is also able to identify variant translocations and loss of DNA sequences, some of which are known to be predictors of poor clinical outcome. To determine the contribution of I-FISH in detecting genetic alterations at diagnosis and during therapy, we summarized our experience in a series of patients with CML and Ph+ ALL studied in a single institution between 2000–2004. A total of 52 patients had both cytogenetic and I-FISH analyses available for review. The 52 patients included 30 patients in chronic phase, 10 patients in accelerated phase, 9 patients in blastic phase, and 3 patients with acute lymphoblastic leukemia (ALL). Sixteen of the 52 patients had newly diagnosed CML, and the remaining 36 patients had studies performed while on imatinib. Conventional cytogenetics detected the Ph-chromosome in 44 patients (85%), whereas I-FISH detected Ph chromosome positivity in all 52 patients (100%). In three of the 16 patients with newly diagnosed disease, I-FISH identified variant translocations in the setting of a normal karyotype. Two of these 3 patients were found to be RT-PCR negative for bcr/abl transcripts. Nineteen of 52 patients (37%) had additional abnormalities detected by karyotype. Nine of these 19 patients (47%) had more than one additional cytogenetic abnormality. The most common abnormalities in the Ph+ clone included: 6 patients with 2 copies of the Ph chromosome, 4 patients with trisomy 21, 2 patients with deletion (20q), 2 patients with isochromosome 17, and 2 patients with trisomy 8. Independent clones with trisomy 8 were noted in an additional 2 patients on imatinib therapy. A total of 12 of the 52 patients (23%) had variant signal patterns by I-FISH; loss of DNA sequences on chromosomes 9 and 22 occurred in 4 and 3 cases respectively and a variant signal pattern involving additional chromosomes was seen in 5 patients. While in general we found a good correlation between the proportion of Ph-positive cells detected by conventional cytogenetics and I-FISH, differences between the two types of analyses were observed in 8 patients. Six patients had a normal karyotype (20 cells analyzed) with positive I-FISH analysis (range 3.2–99%). Two of the 8 patients had a small percentage of Ph-positive metaphases with negative I-FISH. These results underscore the significance of utilizing both conventional cytogenetics and I-FISH in CML patients at diagnosis as well as during therapy. The biologic and clinical implications of the disparity between conventional cytogenetics, I-FISH, and in some cases RT-PCR results are not yet fully realized.