Distribution of common BCR-ABL fusion transcripts and their impact on treatment response in Imatinib treated CML patients: A study from India

Background: Philadelphia chromosome (Ph): Hallmark of CML is caused by reciprocal translocation between chromosomes 9 and 22 resulting in BCR-ABL fusion protein. Most commonly associated breakpoint with CML is M-bcr in exon 13 or exon 14, producing splice variant b2a2 or b3a2 respectively. The distribution of these transcripts and their influence on clinico-hematological parameters is variable. Impact of the fusion transcripts on treatment outcome in Imatinib treated CML patients is still a matter of debate. Aims/settings and design: We conducted this study on 400 CML-CP patients to look for the distribution of fusion transcripts i.e. b3a2 and b2a2, their clinico-hematological profile and impact on treatment response in patients treated with Imatinib. Material and Methods: CML-CP was diagnosed by reverse transcriptase PCR (RT-PCR) for the BCR-ABL fusion transcript. Real-time quantitative PCR (RQ-PCR) was performed on peripheral blood every 3-6 monthly to look for treatment response. Results: The overall frequency of b3a2 transcript was observed in 288 (72%) followed by b2a2 in 104 (26%) and hybrid fusion transcript (b3a2 + b2a2) was seen in 8 (2%) cases. MMR was attained in 198/288 (68.7%) patients with b3a2 transcript and 90/288 (31.3%) patients failed to achieve MMR after 12 months of Imatinib therapy. Among the patients with b2a2 transcript, 44/104 (42.3%) patients achieved MMR and 60/104 (57.7%) patients failed to achieve MMR after 12 months of Imatinib therapy. Conclusions: In conclusion, the frequency of b3a2 transcript was more as compared to b2a2 transcript. MMR was significantly higher in patients with b3a2 transcript as compared to patients with b2a2.

A comprehensive analysis of breakpoint cluster region-abelson fusion oncogene splice variants in chronic myeloid leukemia and their correlation with disease biology.

BACKGROUND: BCR-ABL fusion oncogene is a hallmark of Chronic Myeloid Leukemia (CML). It results due to translocation between chromosome 22 and chromosome 9 [t (9; 22)(q34; q11)]. It gives rise to translation of a 210 KDa chimeric protein (p210), leading to enhanced tyrosine kinase activity and activation of leukemogenic pathways, ultimately causing onset of CML. In case of CML, the classic fusions are b2a2 or b3a2, fusing exon 13 (b2) or exon 14 (b3) of BCR, respectively, to exon 2 (a2) of ABL. The type of BCR-ABL transcripts are thought to be have different prognosis and hence useful in clinical decision-making. The frequencies of different fusion oncogenes associated with leukemia can vary in different ethnic groups and geographical regions due to interplay of genetic variation in different ethnic populations, diverse environmental factors and living style. Moreover, earlier relevant studies from our region were carried out in small subset of patients. Therefore, objective of this study was to find out frequencies of different BCR-ABL splice variants in larger subset of CML patients. METHODS: A nested reverse transcriptase polymerase chain reaction (RT-PCR) was established to detect BCRABL splice variants in 130 CML patients. Sensitivity of RT-PCR and ability to detect BCR-ABL fusion gene in least possible time was studied. RESULTS: BCR-ABL detection using our optimized RTPCR protocol could be completed in 8 hours, starting from RNA extraction to Gel electrophoresis. Sensitivity of RTPCR assay was of the order of 10−6. Out of 130 Pakistani patients, 83 (63.84%) expressed b3a2 while 47 (36.15%) expressed b2a2 transcript. CONCLUSION: Our RT-PCR was proved to be very quick to detect BCR-ABL fusion oncogene in CML patients within one working day. Because of its sensitivity, it can be used to monitor complete molecular response in CML. BCR-ABL RT-PCR and BCR-ABL splice variants frequency in our study differs from other ethnic groups. It shows that ethnic and geographical differences exist in BCR-ABL splice variant frequency, which may have a profound effect on disease biology as well as implications in prognosis and clinical management of BCR-ABL positive leukemias.

Two Cases of Philadelphia Chromosome-negative Essential Thrombocythemia Manifested bcr-abl Gene Rearrangement / 대한임상병리학회지

Discrepant results have been reported in terms of detecting bcr-abl transcripts in patients with essential thrombocythemia that are Philadelphia (Ph) chromosome-negative. We present two cases of Ph chromosome-negative essential thrombocythemia in whom bcr-abl gene rearrangement was detected. In the diagnosis of both cases, they lacked the splenomegaly, anemia and basophilia, and had high platelet counts (948X10(3)/L and 1,329X10(3)/microL, respectively) and normal leukocyte alkaline phosphatase (LAP) scores on admission without any evidence of inflammation, infection, or therapy. They lacked the Philadelphia chromosome characteristic of classical chronic myelogenous leukemia (CML) and had b3a2 transcripts.