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treated with all-trans retinoic acid (ATRA) and at that time the yotype: 46,XX,der(9)t(1;9)(q25;q34)der(9)t(9;?)(q34;?), t(15;17)-fibrinogen and D-dimer were 121 mg/dl and less than (q22;q11)ish. der(9)t(1;9)(q25;q34)(WCP1؉,WCP9؉),t(9;17;15)-1.0 g/ml, respectively. Two weeks following treatment, decreased to 3.8 × 10 3 /ml from 34.5 × 10 3 /ml. Materials and methodsCytogenetic analysis was performed from bone marrow speciIntroduction mens using a routine protocol. 45 Fluorescence in situ hybridization (FISH) was carrried out employing whole chromosome Acute promyelocytic leukemia (APL) has been characterized painting probes (WCP) for chromosome 1, 9, 15 and 17 by atypical morphology (FAB M3) having a balanced translo-(GIBCO/BRL, Gaithersburg, MD, USA), and the APL t(15;17) cation between the long arms of chromosomes 15 and 17, translocation probe (Oncor, Gaithersburg, MD, USA) that t(15;17)(q22q21). In 95% of cases it has been a hallmark cytospecifically identifies the regions of the PML (green) and RAR␣ genetic marker since 1976. 1,2 In recent years, a number of (red) genes involved in the RAR␣/PML gene fusion. All proinvestigators have unveiled the molecular biology underlying cedures were as recommended by the manufacturer. Briefly, the t(15;17) of APL. [3][4][5][6][7] The genes which are involved in this slides were air dried for at least 2 days prior to denaturation, translocation are PML on chromosome 15 and the locus that then denatured in 70% formamide/2 × SSC at 70°C for 10-encodes for retinoic acid receptor alpha (RAR␣) on chromo-15 s each and passed through an ethanol dehydration series. some 17 have been isolated and cloned. 8 Fusion genes are WCP probes were denatured for 10 min at 70°C prior to formed and their abnormal products are PML/RAR␣ and hybridization while the loci-specific translocation probe was RAR␣/PML fusion protein resulting in promyelocytic leukehybridized without denaturation. All probes were hybridized mogenesis. [9][10][11][12][13][14][15][16] Henceforth, this cytogenetic entity has become at 37°C in a moist chamber overnight. The stringency of the a routine diagnostic parameter where both genes can be vispost-hybridization washes were: for the loci-specific probes ualized by fluorescent in situ hybridization. 17 Though t(15,17) 1 × SSPE at 70°C for 5 min and for the WCP probes 50% has been a distinctive translocation, 18,19 a number of variant formamide/2 × SSC (pH 7.0), 2 × SSC/0.1% NP-40 at 45°C. translocations have been observed in APL. In a few cases, WCP probes were spectrum orange or spectrum green fluit has been suggested that the breakpoint on 17q rather than orophore-labeled and the hybridization included unlabeled on 15q is the clinical region in atypical APL, while others have competitor human Cot-1 DNA. The translocation loci specific disagreed. We report an atypical case of APL with previously probe was rhodamine-labeled (RAR␣) and fluorescein-labeled undescribed unusual cytogenetic findings but without an (PML) and detected with rhodamine-labeled anti-digoxigeni...