Comprehensive molecular characterization of a rare case of Philadelphia chromosome-positive acute myeloid leukemia.

The Philadelphia chromosome (Ph) resulting from the t(9;22) translocation generates the oncogenic BCR::ABL1 fusion protein that is most commonly associated with chronic myeloid leukemia (CML) and Ph-positive (Ph+) acute lymphoblastic leukemia (ALL). There are also rare instances of patients (≤1%) with newly diagnosed acute myeloid leukemia (AML) that harbor this translocation (Paietta et al., Leukemia 12: 1881 [1998]; Keung et al., Leuk Res 28: 579 [2004]; Soupir et al., Am J Clin Pathol 127: 642 [2007]). AML with BCR::ABL has only recently been provisionally classified by the World Health Organization as a diagnostically distinct subtype of AML. Discernment from the extremely close differential diagnosis of myeloid blast crisis CML is challenging, largely relying on medical history rather than clinical characteristics (Arber et al., Blood 127: 2391 [2016]). To gain insight into the genomic features underlying the evolution of AML with BCR::ABL, we identified a patient presenting with a high-risk myelodysplastic syndrome that acquired a BCR::ABL alteration after a peripheral blood stem cell transplant. Serial samples were collected and analyzed using whole-exome sequencing, RNA-seq, and ex vivo functional drug screens. Persistent subclones were identified, both at diagnosis and at relapse, including an SF3B1p.Lys700Glu mutation that later cooccurred with an NRASp.Gly12Cys mutation. Functional ex vivo drug screening performed on primary patient cells suggested that combination therapies of ABL1 with RAS or PI3K pathway inhibitors could have augmented the patient's response throughout the course of disease. Together, our findings argue for the importance of genomic profiling and the potential value of ABL1 inhibitor-inclusive combination treatment strategies in patients with this rare disease.

A half-log increase in BCR-ABL RNA predicts a higher risk of relapse in patients with chronic myeloid leukemia with an imatinib-induced complete cytogenetic response.

PURPOSE: Imatinib induces a complete cytogenetic response (CCR) in most chronic myeloid leukemia patients in chronic phase. Although CCR is usually durable, a minority of patients relapse. Biomarkers capable of predicting those CCR patients with a higher risk of relapse would improve therapeutic management. EXPERIMENTAL DESIGN: To assess whether changes in BCR-ABL RNA levels are a prognostic biomarker predictive of relapse, we regularly monitored transcript levels [every 3 months (median)] in 90 patients with CCR during 49 months (median) of imatinib therapy. RESULTS: Throughout follow-up, the 20 patients with eventual relapse had higher transcript levels than the durable responders. Major molecular response (MMR; >3-log reduction of BCR-ABL RNA) was attained by 76 patients (12 with subsequent relapse) and was a significant predictor of prolonged relapse-free survival (P = 0.0008). A minimal 0.5-log increase in transcripts (before relapse; experienced by 42 patients, 16 with subsequent relapse) conveyed a significantly shorter relapse-free survival (P = 0.0017). Loss of MMR (transcript increase to <2.5-log reduction, before relapse; experienced by 33 patients, 11 with subsequent relapse) was also predictive of shortened relapse-free survival (P = 0.0003). A complete molecular response (undetectable transcripts by nested PCR) was attained by 28 MMR patients (one with subsequent relapse) and conveyed a significantly prolonged relapse-free survival (P = 0.0052). CONCLUSIONS: In chronic myeloid leukemia patients with an imatinib-induced CCR, a minimal half-log increase in BCR-ABL RNA (including loss of MMR) is a significant risk factor for future relapse. The achievement of a complete molecular response imparts longer progression-free survival than the achievement of an MMR.

Quantitative BCR-ABL1 RQ-PCR fusion transcript monitoring in chronic myelogenous leukemia.

The reciprocal Philadelphia translocation between chromosomes 9 and 22 [t(9;22)(q34;q11)] creates a BCR-ABL1 fusion protein that occurs in approximately 95% of cases of chronic myelogenous leukemia (CML), 15% of cases of adult acute lymphoblastic leukemia, and 5% of adult cases of acute myeloid leukemia. The BCR-ABL1 protein is a constitutively activated tyrosine kinase that induces and maintains the neoplastic phenotype in these leukemias. PCR-based methods to identify and quantitate the tumor-specific BCR-ABL1 RNA have been shown to be an ultrasensitive diagnostic/prognostic tool for Philadelphia-positive leukemias. A novel tyrosine kinase inhibitor (TKI), imatinib, has been confirmed as an effective targeted treatment in most CML patients. A consensus goal for TKI treatment is to achieve a major molecular response (MMR), defined as a 3-log (1,000-fold) reduction in BCR-ABL1 transcripts. Patients who achieve an MMR have been shown to have a significantly reduced risk of disease progression. Conversely, increasing post-therapy BCR-ABL1 RNA levels convey a significantly increased risk of disease progression. The early identification of these high-risk patients may allow early changes to the therapeutic strategy, before frank relapse. Thus, quantitative measurement of BCR-ABL1 transcripts in blood and bone marrow both aids in the initial diagnosis of CML and is essential for routine post-therapy minimal residual disease monitoring. We describe here a method for quantitating BCR-ABL1 transcripts in peripheral blood or bone marrow of CML patients using real-time quantitative reverse transcription PCR (RQ-PCR).