RESUMO
Background: Acute promyelocytic leukemia (APL) is characterized cytogenetically by t(15;17) (q22;q21) and its molecular consequence, fusion of PML and RAR_ genes. The detection of this genetic marker confirms the diagnosis and allows monitoring of the leukemic clone during treatment, which has prognostic value. Cytogenetics fails in some cases due to the absence of metaphases in cultures or their bad morphology. Southern blot and PCR methods require trained personnel and adequate equipment. FISH method allows the identification of chromosomic rearrangements in 24 to 48 h and is simple to set up in a cytogenetics laboratory. Aim: To evaluate the FISH method to detect PML/RAR_ fusion, compared to cytogenetic analysis. Patients and methods: Fifteen bone marrow specimens from APL patients with previous cytogenetic analysis were studied, using a commercial probe to detect PML/RAR_ fusion. Results: We obtained a normal cut-off value of 9.1 percent. Specificity and sensibility were 100 percent. Six positive cytogenetic cases at diagnosis were FISH positive. Six negative cytogenetic cases, one APL at diagnosis and five normal controls were FISH negative. One case in remission, that was negative by cytogenetics, was positive near the cut-off value by FISH. Two other cases in remission, not conclusive by cytogenetics, were negative by FISH. Conclusions: FISH is a reliable, rapid and relatively low cost method that can be used as an adjunct to conventional cytogenetics