Molecular cytogenetic characterization of Philadelphia-negative rearrangements in chronic myeloid leukemia patients

Chronic myeloid leukemia-from the Philadelphia chromosome to specific target drugs: A literature review

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm and was the first neoplastic disease associated with a well-defined genotypic anomaly - the presence of the Philadelphia chromosome. The advances in cytogenetic and molecular assays are of great importance to the diagnosis, prognosis, treatment, and monitoring of CML. The discovery of the breakpoint cluster region (BCR)-Abelson murine leukemia (ABL) 1 fusion oncogene has revolutionized the treatment of CML patients by allowing the development of targeted drugs that inhibit the tyrosine kinase activity of the BCR-ABL oncoprotein. Tyrosine kinase inhibitors (known as TKIs) are the standard therapy for CML and greatly increase the survival rates, despite adverse effects and the odds of residual disease after discontinuation of treatment. As therapeutic alternatives, the subsequent TKIs lead to faster and deeper molecular remissions; however, with the emergence of resistance to these drugs, immunotherapy appears as an alternative, which may have a cure potential in these patients. Against this background, this article aims at providing an overview on CML clinical management and a summary on the main targeted drugs available in that context.

Prognostic significance of a normal karyotype in adult patients with BCR-ABL1-positive acute lymphoblastic leukemia in the tyrosine kinase inhibitor era

OBJECTIVE

The occurrence of cryptic Philadelphia (Ph) chromosome translocation is rare in BCR-ABL1-positive acute lymphoblastic leukemia (BCR-ABL1+ ALL) and is of unknown significance in the tyrosine kinase inhibitor (TKI) era.

METHODS

We retrospectively studied a series of adult patients receiving TKI-based therapy to evaluate the prognostic impact of the normal karyotype (NK) (n=22) in BCR-ABL1+ ALL by comparison with the isolated Ph+ karyotype (n=54).

RESULTS

There were no statistically significant differences in clinical characteristics and complete remission rate between the two groups. Compared with the isolated Ph+ group, the NK/BCR-ABL1+ group had a higher relapse rate (55.0% versus 29.4%, p=0.044). Overall survival (OS) and disease-free survival (DFS) were significantly shorter in the NK/BCR-ABL1+ group than in the isolated Ph+ group [median OS: 24.5 versus 48.6 (months), p=0.013; median DFS: 11.0 (months) versus undefined, p=0.008]. The five-year OS and DFS for patients with NK/BCR-ABL1+ were 19.2% and 14.5%, respectively; those for patients with isolated Ph+ were 49.5% and 55.7%, respectively. Thirty-four (44.7%) patients underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) in this study. Among the patients who received allo-HSCT, the median OS and DFS in the NK/BCR-ABL+ group (n=9) were 35.5 and 27.5 months, respectively, while those in the isolated Ph+ group (n=25) were undefined. There was a trend of significant statistical difference in the OS between the two subgroups (p=0.066), but no significant difference in the DFS. Multivariate analysis revealed that NK was independently associated with worse OS and DFS in BCR-ABL1+ ALL patients [Hazard ratio (HR) 2.256 (95% confidence interval (CI), 1.005-5.066), p=0.049; HR 2.711 (95% CI, 1.319-5.573), p=0.007].

CONCLUSION

Our results suggest that the sub-classification of an NK could be applied in the prognostic assessments of BCR-ABL1+ ALL. In addition, allo-HSCT should be actively performed to improve prognosis in these patients.

Chronic Myeloid Leukemia with cryptic Philadelphia translocation and extramedullary B-lymphoid blast phase as an initial presentation

Chronic Myeloid Leukemia (CML) is a clonal myeloproliferative neoplasm (MPN) characterized by the presence of a reciprocal translocation between the long arms of chromosomes 9 and 22, t(9;22)(q34:q11), resulting in fusion of the break point cluster region (BCR) with the ABL gene, which forms an oncogene, the transcript of which is an oncoprotein with a tyrosine kinase function. In the great majority of CML; BCR/ABL1 is cytogenetically visualized as t(9;22); giving rise to the Ph chromosome, harboring the chimeric gene. Cryptic or masked translocations occur in 2-10% patients with no evidence for the BCR/ABL rearrangement by conventional cytogenetics but are positive by Fluorescence in Situ Hybridization (FISH) and/or reverse transcriptase polymerase chain reaction (RT-PCR). These patients are described as Philadelphia negative (Ph negative) BCR/ABL1-positive CML with the chimeric gene present on the derivative chromosome 22, as in most CML cases, or alternatively on the derivative 9 in rare occasions. In the majority of cases, CML is diagnosed in the chronic phase; it is less frequently diagnosed in accelerated crises, and occasionally, its initial presentation is as acute leukemia. The prevalence of extramedullary blast phase (BP) has been reported to be 7-17% in patients with BP. Surprisingly, no extramedullary blast crises of B-lymphoid lineage have been reported before among cases of CML as the initial presentation. We report an adult male diagnosed as CML-chronic phase when he was shortly presented with treatment-naive extramedullary B-lymphoid blast crises involving multiple lymph nodes, with no features of acceleration or blast crises in the peripheral blood (PB) and bone marrow (BM). In addition the patient had variant/cryptic Philadelphia translocation. This is the first report of CML, on the best of our knowledge, with extramedullary B-lymphoid blast phase, as initial presentation, that showed a cryptic Ph translocation. (www.actabiomedica.it)

Cryptic BCR-ABL fusion gene as variant rearrangement in chronic myeloid leukemia: molecular cytogenetic characterization and influence on TKIs therapy

At diagnosis, about 5% of Chronic Myeloid Leukemia (CML) patients lacks Philadelphia chromosome (Ph), despite the presence of the BCR/ABL rearrangement. Two mechanisms have been proposed about the occurrence of this rearrangement: the first one is a cryptic insertion between chromosomes 9 and 22; the second one involves two sequential translocations: a classic t(9;22) followed by a reverse translocation, which reconstitutes the normal morphology of the partner chromosomes. Out of 398 newly diagnosed CML patients, we selected 12 Ph-negative cases. Six Ph-negative patients treated with tyrosine kinase inhibitors (TKIs) were characterized, in order to study the mechanisms leading to the rearrangement and the eventual correlation with prognosis in treatment with TKIs. FISH analysis revealed cryptic insertion in 5 patients and classic translocation in the last one. In more detail, we observed 4 different patterns of rearrangement, suggesting high genetic heterogeneity of these patients. In our cases, the BCR/ABL rearrangement mapped more frequently on 9q34 region than on 22q11 region, in contrast to previous reports. Four patients, with low Sokal risk, achieved Complete Cytogenetic Response and/or Major Molecular Response after TKIs therapy. Therapy resistance was observed in one patient with duplication of BCR/ABL rearrangement and in another one with high risk. Even if the number patient is inevitably low, we can confirm that the rare Ph-negative CML patients do not constitute a “warning” category, meanwhile the presence of further cytogenetic abnormalities remains an adverse prognostic factor even in TKI era.

Comprehensive Molecular Analyses in a Case of Masked Philadelphia Chronic Myeloid Leukemia

Here, we report the case of an 80-year-old woman with masked Philadelphia chronic myeloid leukemia (Ph CML). At diagnosis, qualitative PCR demonstrated the presence of a typical e14a2 configuration, and chromosome analysis showed an apparently normal female karyotype. However, FISH with BCR-ABL1 dual fusion probes gave a positive signal in 152/200 analyzed nuclei, with the fusion signal detected on the long arm of a cytogenetically normal chromosome 9. Using locus-specific probes for chromosome 9 and 22 telomeres, a third chromosome involvement was excluded. Furthermore, microarray analysis from the same specimens showed a normal result. Due to a high Charlson Comorbidity Index, the patient was treated with a reduced dose of imatinib, achieving a rapid hematological response after 1 month. However, after 6 months of imatinib therapy, she had to be considered as warning (Ph+ 26.5%, BCR-ABL1 >1%) according to the European LeukemiaNet 2013 recommendations. In conclusion, we confirmed the importance of a combination of cytogenetic and molecular techniques for the diagnosis and therapy monitoring of masked Ph CML, but, different from what has been reported in the literature so far, we cannot completely exclude the fact that the unusual cytogenetic pattern of this patient may have negatively influenced her response to tyrosine kinase inhibitor therapy.

Chronic myeloid leukemia: Relevance of cytogenetic and molecular assays

Chronic myeloid leukemia (CML) is the prototype cytogenetic malignancy. Even before the development of basic G- and R-banding techniques, CML was found to be associated with a persistent chromosomal abnormality, the Philadelphia (Ph) chromosome. Banding technology later showed the marker chromosome to be a translocation between the breakpoint cluster region (BCR) on chromosome 22q11.2 and the Abelson proto-oncogene (ABL) on chromosome 9q34. Further advances in cytogenetic and molecular biology have also contributed to the understanding, diagnosis, and treatment of CML. Fluorescent in situ hybridization (FISH) has revealed cryptic translocations in most cases of Ph-negative CML. Additional rare chromosomal variant translocations have been discovered as well. The understanding of cytogenetic and molecular physiopathology of CML has led to the use of tyrosine kinase inhibitors as treatment for this disease with spectacular success. Over the 40 years since being identified as the first cytogenetic disease, CML has become the greatest success in translating the basic science of oncology into the treatment of patients with cancer. In this review we will not only summarize the biology of CML, recent progress in the delineation of mechanisms and treatment strategies, but also we will discuss the laboratory tools used for diagnosing CML, for monitoring during treatment and for revealing point mutations and additional chromosomal abnormalities. In doing so, we will describe in detail our individual research on CML, identifying why and how these tests were performed to help to explain CML subgroups and clinical significance of additional chromosomal abnormalities.

Assessment of interleukin 1β serum level in different responder groups and stages of chronic myeloid leukemia patients on imatinb mesylate therapy

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the presence of an acquired mutation which affects the hematopoietic stem cell, leading to a striking overproduction of immature granulocytes. The first important clue to its pathogenesis the Philadelphia chromosome created by a reciprocal translocation between chromosomes 9 and 22 (t [9; 22] [q34; q11]). The development of the BCR-ABL-targeted imatinib mesylate represents a paradigm shift in the treatment of CML. Imatinib displays inhibitory activity against other kinase(s) that play a role in monocyte/macrophage development. Accordingly many studies revealed the role of cytokines in pathophysiology of myeloid neoplasia including participation of IL-1β in the pathogenesis of CML. This study designed to assess the behavior of IL-1β through newly diagnosed patients, different responders groups (optimal, suboptimal and failure cytogenetic response) and advanced stages (acceleration and crisis groups) of CML Iraqi patients whom receiving Imatinib mesylate (tyrosine kinase inhibitor), trying to elucidate the role of immunity in pathophysiology of CML disease development and treatments. In this study 96 Iraqi CML patients under imatinib mesylate treatment categorized by complete blood picture and fluorescent in situ hybridization analysis into different response groups and stages, then used an enzyme linked immunosorbent assay technique to assess serum level of IL-1β in each response group and advance stage (acceleration and transformed) of CML patients, in comparison to level in 32 healthy control subjects and 32 newly diagnosed CML. Out of 128 patients the mean serum of interleukin 1β level (pg/ml) for the newly diagnosed, optimal responded, suboptimal responded, failure cytogenetic and advance stage of CML were 6.53 ± 3.81, 18.47 ± 4.29, 18.69 ± 3.03, 5.73 ± 2.44, and 18.10 ± 3.10, respectively. While healthy was 12.17 ± 3.44. The measurement of IL-1β before and during treatment of CML patients may contribute to the early identification of responder and non responder patients, and help in the earlier choice and/or design of alternative therapeutic strategies.

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

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.