Acute promyelocytic leukemia: the study of t(15;17) translocation by fluorescent in situ hybridization, reverse transcriptase-polymerase chain reaction and cytogenetic techniques

Acute promyelocytic leukemia (AML M3) is a well-defined subtype of leukemia with specific and peculiar characteristics. Immediate identification of t( 15;17) or the PML/RARA gene rearrangement is fundamental for treatment. The objective of the present study was to compare fluorescent in situ hybridiz ation (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR) and karyotyping in 18 samples (12 at diagnosis and 6 after treatment) from 13 A ML M3 patients. Bone marrow samples were submitted to karyotype G-banding, FISH and RT-PCR. At diagnosis, cytogenetics was successful in 10 of 12 samp les, 8 with t(15;17) and 2 without. FISH was positive in 11/12 cases tone h ad no cells for analysis) and positivity varied from 25 to 93% (mean: 56%). RT-PCR was done in 6/12 cases and all were positive. Four of 8 patients wi th t(15;17) presented positive RT-PCR as well as 2 without metaphases. The lack of RT-PCR results in the other samples was due to poor quality RNA. Wh en the three tests were compared at diagnosis, karyotyping presented the tr anslocation in 80% of the tested samples while FISH and RT-PCR showed the P ML/ RARA rearrangement in 100% of them. Of 6 samples evaluated after treatm ent, 3 showed a normal karyotype, 1 persistence of an abnormal clone and 2 no metaphases. FISH was negative in 4 samples studied and 2 had no material for analysis. RT-PCR was positive in 4 (2 of which showed negative FISH, i ndicating residual disease) and negative in 2. When the three tests were co mpared after treatment, they showed concordance in 2 of 6 samples or, when there were not enough cells for all tests, concordance between karyotype an d RT-PCR in one. At remission, RT-PCR was the most sensitive test in detect ing residual disease, as expected (positive in 3/6 samples). An incidence o f about 40% of 5 ' breaks and 60% of 3 ' breaks, i.e., bcr3 and bcr1/bcr2, respectively, was observed.