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Imatinib mesylate blocks the activity of three protein tyrosine kinases: ABL, KIT, and platelet-derived growth factor receptor β (PDGFRB). These kinases have crucial roles in chronic myelogenous leukemia (ABL), gastrointestinal stromal tumors (KIT), and certain myeloproliferative diseases (PDGFRB). The first two types of neoplasms have been shown to respond to imatinib mesylate. This article reports that in four patients, a myeloproliferative disorder involving a rearranged PDGFRB gene also responded to the drug. The association of leukemia, eosinophilia, and abnormalities of chromosome 12p13 was originally reported by Keene et al. in 1987 1 ; two of the four patients included in that report also had translocations involving chromosome 5q3. Subsequently, Golub et al. 2 showed that the previously described t(5;12)(q31–q33;p13) chromosomal abnormality, characteristic of some cases of chronic myelomonocytic leukemia, was associated with a fusion gene linking TEL (now known as ETV6 ) with platelet-derived growth factor receptor beta ( PDGFRB ). At least 34 cases of chronic myeloproliferative disease associated with a t(5;12)(q31–q33;p13) translocation have now been reported, 3 and the PDGFRB gene is known . . .

Purpose Approximately 1 – 2% of chronic myeloid leukemia (CML) patients harbor atypical BCR-ABL1 transcripts that cannot be monitored by real-time quantitative PCR (RT-qPCR) using standard methodologies. Within the European Treatment and Outcome Study (EUTOS) for CML we established and validated robust RT-qPCR methods for these patients. Methods BCR-ABL1 transcripts were amplified and sequenced to characterize the underlying fusion. Residual disease monitoring was carried out by RT-qPCR with specific primers and probes using serial dilutions of appropriate BCR-ABL1 and GUSB plasmid DNA calibrators. Results were expressed as log reduction of the BCR-ABL1/GUSB ratio relative to the patient-specific baseline value and evaluated as an individual molecular response (IMR). Results In total, 330 blood samples (2–34 per patient, median 8) from 33 CML patients (19 male, median age 62 years) were analyzed. Patients expressed seven different atypical BCR-ABL1 transcripts (e1a2, n  = 6; e6a2, n  = 1; e8a2, n  = 2; e13a3, n  = 4; e14a3, n  = 6; e13a3/e14a3, n  = 2; e19a2, n  = 12). Most patients (61%) responded well to TKI therapy and achieved an IMR of at least one log reduction 3 months after diagnosis. Four patients relapsed with a significant increase of BCR-ABL1/GUSB ratios. Conclusions Characterization of atypical BCR-ABL1 transcripts is essential for adequate patient monitoring and to avoid false-negative results. The results cannot be expressed on the International Scale (IS) and thus the common molecular milestones and guidelines for treatment are difficult to apply. We, therefore, suggest reporting IMR levels in these cases as a time-dependent log reduction of BCR-ABL1 transcript levels compared to baseline prior to therapy.

Membrane transporters are important determinants of drug bioavailability. Their expression and activity affect the intracellular drug concentration in leukemic cells impacting response to therapy. Pharmacogenomics represents genetic markers that reflect allele arrangement of genes encoding drug transporters associated with treatment response. In previous work, we identified SNP rs460089 located in the promotor of SLC22A4 gene encoding imatinib transporter OCTN1 as influential on response of patients with chronic myeloid leukemia treated with imatinib. Patients with rs460089-GC pharmacogenotype had significantly superior response to first-line imatinib treatment compared to patients with rs460089-GG. This study investigated whether pharmacogenotypes of rs460089 are associated with sustainability of treatment-free remission (TFR) in patients from the EUROpean Stop Kinase Inhibitor (EURO-SKI) trial. In the learning sample, 176 patients showed a significantly higher 6-month probability of molecular relapse free survival (MRFS) in patients with GC genotype (73%, 95% CI: 60–82%) compared to patients with GG (51%, 95% CI: 41–61%). Also over time, patients with GC genotype had significantly higher MRFS probabilities compared with patients with GG (HR: 0.474, 95% CI: 0.280-0.802, p  = 0.0054). Both results were validated with data on 93 patients from the Polish STOP imatinib study. In multiple regression models, in addition to the investigated genotype, duration of TKI therapy (EURO-SKI trial) and duration of deep molecular response (Polish study) were identified as independent prognostic factors. The SNP rs460089 was found as an independent predictor of TFR.

This work investigated patient-specific genomic BCR-ABL1 fusions as markers of measurable residual disease (MRD) in chronic myeloid leukaemia, with a focus on relevance to treatment-free remission (TFR) after achievement of deep molecular response (DMR) on tyrosine kinase inhibitor (TKI) therapy. DNA and mRNA BCR-ABL1 measurements by qPCR were compared in 2189 samples (129 patients) and by digital PCR in 1279 sample (62 patients). A high correlation was found at levels of disease above MR4, but there was a poor correlation for samples during DMR. A combination of DNA and RNA MRD measurements resulted in a better prediction of molecular relapse-free survival (MRFS) after TKI stop (n = 17) or scheduled interruption (n = 25). At 18 months after treatment cessation, patients with stopped or interrupted TKI therapy who were DNA negative/RNA negative during DMR maintenance (green group) had an MRFS of 80% and 100%, respectively, compared with those who were DNA positive/RNA negative (MRFS = 57% and 67%, respectively; yellow group) or DNA positive/RNA positive (MRFS = 20% for both cohorts; red group). Thus, we propose a “traffic light” stratification as a TFR predictor based on DNA and mRNA BCR-ABL1 measurements during DMR maintenance before TKI cessation.