Mutagenesis Advance Access published online on November 21, 2008
Mutagenesis, doi:10.1093/mutage/gen063
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Cytogenetic and molecular analysis of MLL rearrangements in acute lymphoblastic leukaemia survivors
1Departamento de Genética 2Departamento de Pediatria e Puericultura, Faculdade de Medicina de Ribeirão Preto-USP 3Departamento de Biologia, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto-USP, Universidade de São Paulo, Avenue Bandeirantes 3900, 14040-901 Ribeirão Preto, São Paulo, Brazil
The successful treatment of paediatric malignancies by multimodal therapy has improved outcomes for children with cancer, especially those with acute lymphoblastic leukaemia (ALL). Second malignant neoplasms, however, represent a serious complication after treatment. Depending on dosage, 2–12% of patients treated with topoisomerase II inhibitors and/or alkylating agents develop treatment-related acute myeloid leukaemia characterized by translocations at 11q23. Our goal was to study MLL rearrangements in peripheral lymphocytes using cytogenetic and molecular methods in order to evaluate the late effects of cancer therapy in patients previously treated for childhood ALL. Chromosomal rearrangements at 11q23 were analysed in cytogenetic preparations from 49 long-term ALL survivors and 49 control individuals. Patients were subdivided depending on the inclusion or omission of topoisomerase II inhibitors (VP-16 and/or VM-26) in their treatment protocol. The statistical analysis showed significant (P = 0.007) differences between the frequency of translocations observed for the groups of patients and controls. These differences were also significant (P = 0.006) when the groups of patients (independent of the inclusion of topoisomerase II inhibitors) and controls were compared (P = 0.006). The frequencies of extra signals, however, did not differ between groups of patients and controls. Several MLL translocations were detected and identified by inverse polymerase chain reaction, followed by cloning and sequencing. Thirty-five patients (81%) presented putative translocations; among those, 91% corresponded with t(4;11) (q21;q23), while the other 9% corresponded with t(11;X), t(8;11)(q23;q23) and t(11;16). Our results indicate an increase in MLL aberrations in childhood ALL survivors years after completion of therapy. The higher frequency in this cohort might be associated with therapy using anti-tumoural drugs, independent of the inclusion of topoisomerase II inhibitors. Even though the biological significance of these rearrangements needs further investigation, they demonstrate a degree of genome instability, indicating the relevance of cytogenetic and molecular studies during the follow-up of patients in complete clinical remission.
* To whom correspondence should be addressed. Hospital das Clínicas da Faculdade de Medicina de Rebeirão Preto-USP, Laboratório de Pediatria-Bloco G, Avenue Bandeirantes 3900, Bairro Monte Alegre, CEP, 14048-900, Ribeirão Preto, São Pauto, Brazil. Tel: +55 16 36022651; Fax: +55 16 36022700; Email: marsol{at}rge.fmrp.usp.br
Received on August 10, 2008; revised on October 3, 2008; accepted on October 28, 2008.