Molecular cytogenetic findings supporting the evidence of a biclonal origin in acute myeloid leukemia

Abstract

Dear Editor, Hematologic malignancies are clonal disorders arising from a single mutated cell. However, the detection of more than one cytogenetically unrelated abnormal clone has occasionally been reported [3]. Cytogenetic biclonality has rarely been observed in adult acute myeloid leukemia (AML); in none of the cases reported in literature has a molecular cytogenetic analysis been performed [1, 5]. We report a case of adult AML-M2 at diagnosis with biclonal cytogenetic abnormalities represented by two novel translocations. The first clone showed a translocation t(1;2)(p23;p21), while in the second clone, we observed an unbalanced t(11;12)(q13;p13). Conventional cytogenetic analyses were carried out on bone marrow samples at diagnosis according to standard methods [2]. Multicolor fluorescence in situ hybridization (M-FISH) [4] was performed following the manufacturer’s protocol (SpectraVysion, Vysis). Chromosome preparations for FISH experiments were hybridized in situ with appropriate BAC/PAC clones, selected according to the University of California Santa Cruz database. The patient, a 39-year-old man, was admitted to our department for fever and weakness. Peripheral blood examination revealed Hb 9.1 g/dl, WBC 7.3×10/l with 88% of blast cells and platelets 120×10/l. A bone marrow aspiration showed 68% blasts. According to FAB classification, these findings were consistent with AML, M2 subtype. The immunophenotypic analysis revealed CD13, CD33, CD34, CD117; blast cell population was homogeneous in terms of morphological and immunophenotypic features. Conventional cytogenetic analysis showed the following karyotype: 46,XY,t(1;2)(p21;p22)[17]/46,XY,add (12)(p13)[5]/46,XY[3]. The patient started induction treatment with daunorubicin and cytosine arabinoside but did not achieve complete remission (CR). He was then administered the fludarabine AraC G-CSF (FLAG) regimen as salvage therapy, but he did not achieve CR. He subsequently refused further treatments and was no longer to be found for follow-up. M-FISH showed the presence of two abnormal unrelated clones in addition to a normal clone of 46,XY. These experiments confirmed the occurrence of a t(1;2) in one clone and clarified that, in the second clone, the abnormal chromosome defined as add(12) by conventional cytogenetics was a der(12)t(11;12) (Fig. 1a–b). FISH experiments, aimed at precisely defining the breakpoints of the t(1;2) rearrangement, disclosed the loss of 2.6and 2.1-Mb sequences of chromosomes 1 and 2, respectively. The distal breakpoint on 1p was mapped inside the BAC RP11-168A23 (1p21.3), as it gave a faint signal on der(2) in addition to a signal on normal chromosome 1 (Fig. 1c). The proximal breakpoint on 1p was delimited by RP11-472P1 and RP11-825C16 (1p21.2), as the former clone was deleted, whereas the latter hybridized on both chromosomes 1 and der(1) (Fig. 1c). Seven known genes are located in this interval. The distal breakpoint of the chromosome 2 deletion was localized between RP11-803B18 (2p23.3), which gave a signal on der(1), and RP11-443B20 (2p23.3), which hybridized only on normal chromosome 2 (Fig. 1d). The region encompassed by RP11-106G13 and RP11-692D20 (2p23.3) delimited the proximal breakpoint on 2p; in fact, the former failed to reveal any signal on the derivative chromosomes, whereas the latter hybridized on der(2) in addition to the normal chromosome 2 (Fig. 1d). A total of 29 known genes were lost. F. Albano . G. Specchia (*) . V. Liso Department of Hematology, University of Bari, Policlinico, Piazza Giulio Cesare 11, 70124 Bari, Italy e-mail: g.specchia@ematba.uniba.it Tel.: +39-80-5478711 Fax: +39-80-5508369