Molecular Monitoring of Residual Disease in Chronic Myeloid Leukemia by Genomic DNA Compared with Conventional mRNA Analysis

Abstract

Translocation t(9;22) , which produces the BCR-ABL gene , is pathognomonic of chronic myeloid leukemia. For clinical purposes , the amount of chimeric transcript is considered proportional to the leukemic clone; thus , mRNA is commonly used for molecular monitoring of patients. However , there is no consensus regarding the degree of increase in mRNA that should cause concern or whether the absence of transcript indicates a "cure." In this study , we analyzed 57 samples from 10 chronic myeloid leukemia patients undergoing imatinib treatment. For each sample, we compared BCR-ABL mRNA levels with the actual proportion of leukemic cells , which were measured through a novel genomic approach based on the quantitative amplification of DNA breakpoints. The two approaches gave similar patterns of residual disease , and the majority of patients were still positive after an average treatment period of 2 years. Nevertheless , in one of two patients with confirmed undetectable levels of chimeric transcript , DNA still revealed the persistence of leukemic cells at 42 months. These findings appear to justify the clinical practice of maintaining imatinib treatment indefinitely. However , the absence of leukemic DNA (observed in 1 of 10 patients) could be used to identify possible candidates for drug discontinuation. In conclusion , DNA analysis proved to be a reliable index of residual disease with potential applications in the field of clinical diagnostics and research. (J Mol Diagn

In search of the original leukemic clone in chronic myeloid leukemia patients in complete molecular remission after stem cell transplantation or imatinib

“…In 1 of the 5, gBCR-ABL was detected in all (n ϭ 5) FU samples tested; 4 of the 5 patients became gBCR-ABL-negative with continuing IM therapy. These results expand on the findings from a recent publication 35 and indicate that, in IM-treated patients, absence of transcripts should not be interpreted as absence of the leukemic clone. In addition, our results fit with the reported continuing reduction in amount of residual disease (measured by mRNA) in long-term treatment with IM, 17 and demonstrate such a reduction in a proportion of the patients previously classified as CMR by BCR-ABL mRNA quantification.…”

Do we have to kill the last CML cell?

“…This has led us and others to investigate the use of patient-specific BCR-ABL genomic DNA breakpoints as an investigational test to improve the lower limit of detection of MRD. [17][18][19][20] In order to perform patient-specific DNA PCR in CML, it is necessary to identify the BCR-ABL fusion region and to design primers for each patient to ensure specificity for the unique fusion sequence (Figure 1). The use of a patient-specific DNA sequence as the marker of the leukaemic clone is well established in acute lymphoblastic leukaemia, in which the target sequence is either the immunoglobulin gene or the T cell receptor gene rearrangement.…”

Molecular genetic evaluation of myeloproliferative neoplasms

“…DNA‐based nested quantitative PCR techniques to detect BCR‐ABL1 sequences are more sensitive (sensitivity ≈ 10 −6 vs . 10 −5 ), but these methodologies are labor‐intensive and currently not optimized for the clinical laboratory .…”