Molecular diagnosis and monitoring in the clinical management of patients with chronic myelogenous leukemia treated with tyrosine kinase inhibitors

Abstract

The well-established molecular pathogenesis of chronic myelogenous leukemia (CML) and its consequences for laboratory testing and clinical management illustrate a classic paradigm for the importance of molecular diagnostics in targeted drug therapy. The success of the tyrosine kinase inhibitor (TKI), imatinib, as the currently recommended first-line treatment of early chronic phase CML has both fueled the need for timely and reproducible molecular testing of the BCR-ABL1 fusion transcript in diagnosis and monitoring as well as necessitated the detection of kinase domain mutations that confer resistance to this agent. As, ongoing research continues to refine guidelines for monitoring residual disease in patients undergoing TKI therapy, an understanding of molecular technologies and their interpretation is critical. This review summarizes the molecular strategies that are currently employed in the initial diagnosis and subsequent management of CML patients maintained on TKI therapy. Am. J. Hematol. 83:296-302, 2008. V V C 2007 Wiley-Liss, Inc. Molecular Basis of CMLChronic myelogenous leukemia (CML), which comprises 15-20% of all adult leukemias, is the first human neoplasm to be associated with a single, specific, acquired oncogenic mutation, namely the fusion of ABL1 (chromosome 9) and BCR (chromosome 22) genes. CML is a clonal stem cell disease that results in expanding myelopoiesis, with a natural history characterized by three phases: chronic (CP), accelerated (AP), and blast phase (BP); BP is synonymous with blast crisis. Classically, the chronic (or stable) phase lasts for three to five years, during which myeloid hyperplasia results in circulating granulocytes in all stages of maturation with associated basophilia. While the typical triphasic nature of CML is well accepted [1], there is significant variability in the published literature as to the specific criteria for diagnosing AP and, to some degree, BP. Nonetheless, in AP, myeloid elements begin to lose the ability to differentiate with an inevitable evolution to BP that is characterized by acute leukemia of predominantly myeloid (70%), but not uncommonly lymphoid (30%), phenotype [2].The acquired cytogenetic abnormality that is essentially diagnostic of CML in the appropriate hematologic context is the Philadelphia chromosome (Ph) [3], a truncated chromosome 22 resulting from a reciprocal t(9;22)(q34;q11) translocation. This translocation, which fuses the BCR and ABL1 genes [4], has been identified as the initial transforming event in CML pathogenesis, although some data suggest that it may be preceded by clonal hematopoiesis [5]. The BCR gene encodes a cytoplasmic protein that is thought to act as a tumor suppressor in the Wnt signaling pathway [6] as well as function in the cellular trafficking of growth factor receptors [7]. ABL1, which localizes to the nucleus, plasma membrane, and cytoskeleton, encodes a nonreceptor tyrosine kinase involved in normal hematopoiesis. The resultant chimeric fusion protein, located in the cytosol, has constitutively ...

Cytogenetic & molecular analyses in adult chronic myelogenous leukaemia patients in north India

“…Cytogenetic study and qualitative RT-PCR have prime importance at the time of diagnosis, whereas serial quantitative RQ-PCR is recommended for therapeutic monitoring45.…”

“…CML patients with breakpoint in micro bcr (μ-bcr), e19a2 and p230 chimeric protein, may demonstrate prominent neutrophilic and/or thrombocytosis; these should not be diagnosed as chronic neutrophilic leukaemia (CNL) or essential thrombocythaemia (ET)1. Therefore, in the current scenario cytogenetic and molecular analyses of CML patients have become mandatory in order to undertake diagnostic evaluation and monitor/predict response to newer molecular targeted treatment modalities like imatinib mesylate (IM)1–5. Variable frequencies of BCR-ABL fusion transcripts have been reported from different parts of the world26–11; a few documented b2a2 to be more common78, whereas other studies found b3a2 to be more common9–11.…”

RNA quantification using gold nanoprobes - application to cancer diagnostics

“…This translocation - ABL gene (chromosome 9) and BCR gene (chromosome 22) - originates a BCR-ABL fusion gene, leading to the expression of a chimeric BCR-ABL protein with tyrosine-kinase activity [13-15]. The most commonly used procedures for the initial diagnosis and management of CML patients are expensive and time consuming, e.g karyotype analysis, reverse transcriptase polymerase chain reaction analyses (RT-PCR) and fluorescence in-situ hybridization (FISH) [16-18]. Therefore, there is a need for molecular methods able to detect and quantify the BCR-ABL fusion transcripts, which is of paramount relevance when monitoring minimal residual disease and genetic recurrence in patients known to harbor the translocation [19,20].…”

Malleable Immunoglobulin Genes and Hematopathology – The Good, the Bad, and the Ugly

“…2 Allied to its diagnostic utility, molecular analysis is central to contemporary classification and prognostic assignment, 3,4 and it is particularly well suited to testing for minimal residual disease after therapy. 5,6 A variety of molecular phenomena are amenable to routine diagnostic molecular analysis, with an assessment of gene rearrangements currently being the most commonly evaluated phenomenon. Gene rearrangements can be conveniently grouped into two broad categories: physiological and pathological.…”