Complete cytogenetic and molecular response after imatinib treatment for chronic myeloid leukemia in a patient with atypical karyotype and BCR-ABL b2a3 transcript

Molecular Monitoring in Adult Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia with the Variant e13a3 BCR-ABL1 Fusion

Monitoring BCR-ABL1 transcript levels in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) is a widely adopted method to assess response to therapy. However, a small minority of Ph+ ALL patients express variant BCR-ABL1 transcript types, usually due to splicing of alternative BCR or ABL1 exons. Whether patients expressing these rare, variant BCR-ABL1 transcripts have a distinct phenotype or response to therapy is not known due to the limited number of reported cases. Here, we report the presenting features of Ph+ ALL in a young adult with a variant e13a3 BCR-ABL1 fusion. Molecular monitoring reflected the disease response from diagnosis through allogeneic stem cell transplantation which resulted in undetectable e13a3 BCR-ABL1 transcripts. This case highlights the value of molecular monitoring in Ph+ ALL patients with variant BCR-ABL1 transcripts and the requirement for standardization of such assays.

New rapid method to detect BCR-ABL fusion genes with multiplex RT-qPCR in one-tube at a time

Fast identification of BCR-ABL fusion genes is critical for precise diagnosis, risk stratification and therapy scheme selection in leukemia. More convenient methods are needed for quickly detection of the BCR-ABL fusion genes. Multiplex fluorescent reverse transcription quantitative real-time PCR (Multiplex RT-qPCR) methods are developed for detection of the at least 14 subtypes of BCR-ABL fusion genes in one tube at a time by using patients' bone marrow samples. The new Multiplex RT-qPCR method could quickly detect BCR-ABL fusion genes with sensitivity up to 10-10⁶ copies. It can detect the fusion genes in patients' bone marrow samples containing any subtypes of the major bcr (M-bcr) e13a2, e14a2, e13a3 and e14a3, the minor bcr (m-bcr) e1a2 and e1a3, the micro bcr (μ-bcr) e19a2 and e19a3, and the nano bcr (n-bcr) e6a2 and e6a3. The specificity is comparable to the FISH methods. The cutoff for clinical diagnosis of BCR-ABL(+) is also determined by testing in clinical chronic myeloid leukemia samples. This is a new fast method with high sensitivity and specificity for clinical detection of BCR-ABL fusion genes. It will benefit the precise diagnosis, targeted therapy and minimal residual disease (MRD) monitoring in leukemia.

A rare chronic myeloid leukemia case with Philadelphia chromosome, BCR-ABL e13a3 transcript and complex translocation involving four different chromosomes

The so-called Philadelphia (Ph) chromosome is present in more than 90% of chronic myeloid leukemia (CML) patients. Around 5-10% of these patients show complex translocations involving other chromosomes in addition to and/or besides chromosomes 9 and 22. CML cases with fusion transcripts, such as e13a3, in which ABL exon 3 rather than exon 2 has fused to BCR, are extremely rare. Such reported cases with the e13a3 transcript showed the Ph chromosome on karyotype analysis. This study reported a rare Ph chromosome-positive CML case with new complex chromosomal aberrations and an e13a3 BCR-ABL transcript that has yet to be established. A four-chromosome translocation involving chromosomal regions 12p11.2, 19q13.3, 9q34.1 and 22q11.2, besides a trisomy 8 and a derivative chromosome 12, were identified using high resolution multicolor banding. Reverse transcription polymerase chain reaction products showed the presence of BCR-ABL fusion transcript e13a3, and this signifies the major BCR breakpoint. The significance of the observed rearrangements and their possible role in the progression of CML was investigated.

A chronic myeloid leukemia patient with atypical karyotype and BCR-ABL e13a3 transcript caused by complex chromosome rearrangement

Philadelphia (Ph) chromosome as a result of t (9; 22) (q34; q11) is observed in more than 90% of chromic myeloid leukemia (CML) patients. Cases in which the typical Ph chromosome is not visible at the karyotype level comprise 5-10% of CML patients. CML cases with fusion transcripts such as e13a3 in which ABL exon 3 rather than exon 2 has fused to BCR are very rare. Such reported cases with the e13a3 transcript show the Ph chromosome on karyotype analysis. We reported an atypical karyotype CML patient with the e13a3 BCR-ABL transcript caused by complex translocation. Fluorescence in situ hybridization (FISH) analysis of the metaphase led to a precise cytogenetical characterization. The patient showed favorable response to imatinib, and achieved major molecular responses.

Emerging stem cell concepts for imatinib-resistant chronic myeloid leukaemia: implications for the biology, management, and therapy of the disease

Chronic myeloid leukaemia (CML) is a myeloid neoplasm defined by the BCR/ABL oncoprotein that is considered essential for leukaemogenesis and accumulation of neoplastic cells. The BCR/ABL kinase inhibitor imatinib is an effective agent in most patients and can now be regarded as front-line therapy. Hence, intrinsic and acquired resistance to imatinib has been described and is an emerging challenge in clinical practice. While CML stem cells display primary resistance, stem cell subclones may, in addition, acquire imatinib-resistant mutants of BCR/ABL. Other factors that are considered to contribute to stem cell resistance include the genetic background, clonal evolution, additional biological features of subclones, gene amplifications, silencing of tumour suppressor genes and specific pharmacological aspects. In this article, mechanisms of resistance of CML (stem) cells against imatinib and other BCR/ABL inhibitors are discussed, together with strategies to overcome and/or to prevent resistance with available drugs or novel anti-leukaemic approaches.