Some observations on fluorescence in situ hybridization evaluation of chronic myelocytic leukemia.

Cosmid probes specific for the major BCR/ABL rearrangement (commercially available probes) were employed by us to evaluate 134 patients with the clinical diagnosis of chronic myelocytic leukemia (CML). The following represent our main observations: 1) No significant statistical difference regarding a false positive fusion signal was seen in the distribution pattern between the Ph negative (−) cases (110) and the normal controls (3.23 ± 1.97 vs 2.8 ± 1.92, respectively). 2) The mean percentage of cells with a positive fusion signal in the Ph positive (+) CML cases at presentation was 70 ± 12.3 in bone marrow samples (12 cases) and 45 ± 12.4 in blood samples (3 cases). 3) A significant discrepancy was seen between the interphase FISH and cytogenetics data in the monitoring of four out of eight patients post-therapy. The clinical significance of this observation needs to be clarified. 4) Three Ph(−) patients with significant leukocytosis had closely adjacent but not fused signals (20%, 16%, and 20% of cells, respectively, vs. the control: 4%). This may indicate a temporal and spatial association between chromosomes 9 and 22 prior to the BCR/ABL rearrangement (Ph chromosome formation).