Unusual location of BCR-ABL1 fusion sequences in a chronic myeloid leukemia patient

Abstract

We describe a case of a chronic myeloid leukemia patient displaying the chimeric BCR-ABL1 gene on 12p11. Chromosome analysis revealed complex chromosome aberration involving chromosomes 9, 12, and 22. Fluorescence in situ hybridization revealed an unusual signal pattern revealing the BCR-ABL1 fusion signal on chromosome 12, while no reciprocal ABL1-BCR fusion was detected on der(9) chromosome. The relocation of BCR-ABL1 fusion sequences to 12p11 site in our patient represents a rare type of variant translocation, as in almost all patients the chimeric BCR-ABL1 gene is located on der(22) chromosome. Our case illustrates the challenge of recognizing a complex pattern of cytogenetic aberrations that occur with variant t(9;22) and may add further information about clinical significance of unusual variant Ph rearrangements in CML patients receiving tyrosine kinase inhibitor treatment.     

Equivalence of BCR-ABL transcript levels with complete cytogenetic remission in patients with chronic myeloid leukemia in chronic phase

Purpose

Chronic myeloid leukemia (CML) patients are monitored by both cytogenetic and molecular assessments, although present guidelines appear to switch from cytogenetic to molecular criteria. Due to the increasing use of molecular measurements, it was the aim of this work to identify a BCR-ABL level according to the international scale (BCR-ABL^IS) as an equivalent substitute for complete cytogenetic remission (CCyR).

Methods

In total, 1,329 paired data from 557 patients of the German CML-Study IV were evaluated. The data set was divided into a learning set and a validation set. The best cutoff was determined applying a minimal p value approach to the Fisher test.

Results

In the learning set, we found BCR-ABL^IS values between 0.2 and 1.1 % were well suited for predicting a CCyR. In the validation set, the cutoff level of 1 % led to a mean concordance rate of 90.1 %.

Conclusions

Our results suggest that there is no one-to-one cutoff for BCR-ABL^IS representing CCyR, but we advise to use the 1 % BCR-ABL^IS in order to avoid misclassification of CCyR patients.     

Inhibition of apoptosis by BCR-ABL in chronic myeloid leukemia

BCR-ABL expression is presumed to effect clonal expansion in chronic myeloid leukemia (CML) by deregulation of cell proliferation. However, most studies have found that relative rates of cell proliferation are not increased in CML. Moreover, we found that CML progenitors display a normal proliferative response to growth factors and do not manifest greater proliferative potential than normal progenitors. Growth of malignancies depends on an imbalance between the rate of cell production and the rate of cell death. We found that BCR-ABL expression inappropriately prolongs the growth factor-independent survival of CML myeloid progenitors and granulocytes by inhibiting apoptosis, a genetically programmed process of active cell death; inhibition of BCR- ABL expression by antisense oligonucleotides reversed the suppression of apoptosis as well as the enhancement of survival. The decreased rate of programmed cell death appears to be the primary mechanism by which BCR-ABL effects expansion of the leukemic clone in CML.     

Second-generation BCR-ABL inhibitors for frontline treatment of chronic myeloid leukemia in chronic phase

Results from several trials in patients with newly diagnosed chronic myeloid leukemia in chronic phase (CML-CP) of dasatinib and nilotinib, two BCR-ABL inhibitors with higher in vitro potency compared with imatinib, have recently been reported. In this review, the rationale for assessing dasatinib and nilotinib in the frontline setting is discussed and data from clinical trials performed to date are summarized, including single-arm studies and randomized trials compared with imatinib. Overall, both dasatinib and nilotinib have shown superior efficacy compared with imatinib during the first year of treatment and longer-term follow-up is needed to confirm that this superiority is maintained over time. Both agents have also shown favorable tolerability profiles, although distinct patterns of adverse events are seen with each agent. Clinicians now have several effective options to treat patients newly diagnosed with CML-CP and available data suggest that dasatinib and nilotinib represent improved therapeutic options compared with imatinib.     

BCR-ABL inhibitors: Updates in the management of patients with chronic-phase chronic myeloid leukemia

Objectives

This article reviews recent clinical experiences with first-line and second-line second-generation BCR-ABL inhibitors and discusses considerations for selection of therapy for patients with chronic-phase chronic myeloid leukemia.

Methods

We reviewed recent publications on PubMed and abstracts from major congresses relevant to the topic.

Results

Therapeutic options for front-line treatment have increased with the approval of two second-generation BCR-ABL inhibitors, dasatinib and nilotinib. Both agents are also treatment options for patients with resistance or intolerance to front-line imatinib. More recently, bosutinib, ponatinib, and omacetaxine have also been approved for patients with resistance or intolerance to prior therapy.

Discussion

Expanded treatment options coupled with rapidly changing treatment guidelines have led to numerous questions regarding the selection and monitoring of therapy. Common concerns include how to best select therapy based upon patient-specific comorbidities, monitoring and interpretation of treatment outcomes, and optimization of dosing when side effects occur.