Location of the BCR/ABL Fusion Genes on Both Chromosomes 9 in Ph Negative Young CML Patients: An Indian Experience

The BCR/ABL gene rearrangement is cytogenetically visualized in most chronic myeloid leukemia (CML) cases. About 5–10 % of CML patients lack its cytogenetic evidence, however, shows BCR/ABL fusion by molecular methods. We describe two CML patients with Philadelphia (Ph) negative (−ve) and BCR/ABL positive by fluorescence in situ hybridization (FISH). Both the cases were in chronic phase at diagnosis. Conventional cytogenetics and different FISH assays were adopted using BCR/ABL probes. Home-brew FISH assay using bacterial artificial clone (BAC) for BAC-CTA/bk 299D3 for chromosomal region 22q13.31-q13.32 was performed in case 1. Both the patients were Ph-ve. In first case, dual color dual fusion (DCDF)-FISH studies revealed 1 Red (R) 2 Green (G) 1 Fusion (F) signal pattern in 80 % of cells indicating BCR/ABL fusion signals on chromosomes 9 instead of Ph and 2G2F signal pattern in 20 % of cells indicating two BCR/ABL fusions on both chromosomes 9q34 on presentation. In second case, FISH studies revealed the 1R1G1F signal pattern indicating BCR/ABL fusion signals on chromosomes 9 instead of Ph in 100 % of cells at presentation. During follow-up, both the patients exhibited 2G2F signal pattern indicating two BCR/ABL fusions on both chromosomes 9q34, which indicated a clonal evolution in 100 % cells. Both the patients did not achieve therapeutic response. Relocation of BCR/ABL fusion sequence on sites other than 22q11 represents a rare type of variant Ph, the present study highlights the hot spots involved in CML pathogenesis and signifies their implications in Ph−ve BCR/ABL positive CML. This study demonstrated the genetic heterogeneity of this subgroup of CML and strongly emphasized the role of metaphase FISH, especially in Ph−ve CML cases, as it detects variations of the classical t(9;22).     

Successful treatment with nilotinib after imatinib failure in a CML patient with a four-way Ph chromosome translocation and point mutations in BCR/ABL gene

Chronic myelogenous leukemia (CML) is characterized by Philadelphia (Ph) chromosome with a chimeric gene BCR–ABL created by reciprocal t(9:22) (q34;q11) translocation. Variant Ph chromosome translocations involving chromosomes other than 9 and 22 are found in 5–10% of CML cases. We here report a CML patient who carries a four-way Ph chromosome translocation, t(9;22;15;19) (q34;q11;q15;q13). The patient was diagnosed in 1997 and initially treated with hydroxyurea. In 2002, treatment with imatinib, a selective BCR–ABL tyrosine kinase inhibitor (TKI), was started but Ph-positive chromosomes remained at the levels of 42–65%, indicating imatinib failure. In 2006, the point mutations of F359I and L387M were detected in BCR/ABL gene, which may be related to imatinib failure. Treatment with nilotinib, a TKI with high target specificity, was then started which resulted in durable major molecular response. Administration of nilotinib offered an effective treatment in a CML patient with variant Ph chromosome translocations and BCR–ABL point mutations after imatinib failure.     

Chronic myelogenous leukemia: molecular and cellular aspects

Chronic myelogenous leukemia (CML) originates in a pluripotent hematopoetic stem cell of the bone marrow and is characterized by greatly increased numbers of granulocytes in the blood. Myeloid and other hematopoetic cell lineages are involved in the process of clonal proliferation and differentiation. After a period of 4–6 years the disease progresses to acute-stage leukemia. On the cellular level, CML is associated with a specific chromosome abnormality, the t(9; 22) reciprocal translocation that forms the Philadelphia (Ph) chromosome. The Ph chromosome is the result of a molecular rearrangement between the c-ABL proto-oncogene on chromosome 9 and the BCR (breakpoint cluster region) gene on chromosome 22. Most of ABL is linked with a truncated BCR. The BCR/ABL fusion gene codes for an 8-kb mRNA and a novel 210-kDa protein which has higher and aberrant tyrosine kinase activity than the normal c-ABL-coded counterpart. Phosphorylation of a number of substrates such as GAP, GRB-2, SHC, FES, CRKL, and paxillin is considered a decisive step in transformation. An etiological connection between BCR/ABL and leukemia is indicated by the observation that transgenic mice bearing a BCR/ABL DNA construct develop leukemia of B, T, and myeloid cell origin. CML cells proliferate and expand in an almost unlimited manner. Adhesion defects in bone marrow stromal cells have been proposed to explain the increased number of leukemic cells in the peripheral blood. However, findings of our laboratory have shown that the BCR/ABL chimeric protein that is expressed in transfected cells may, under certain conditions, also increase the adhesion to fibronectin via enhanced expression of integrin. Our previous immunocytological studies on the expression of β1 and β2 integrins have found no qualitative differences between normal and CML hematopoietic cells in vitro. Even long-term-cultured CML bone marrow or blood cells continuously express those adhesion molecules that are characteristic of the cytological type. Recent experiments indicate that certain early CML progenitors may adhere to the stromal layer in vitro similarly to their normal counterparts. They cannot be completely removed by long-term culture on allogeneic stromal cells. At present, the only curative therapy is transplantation of allogeneic hematopoietic stem cells. Based on the molecular and cellular state of knowledge of CML, new therapies are being developed. BCR/ABL antisense oligonucleotides, inhibitors of tyrosine kinase, peptide-specific adoptive immunotherapy or peptide vaccination, and restoration of hematopoiesis by autologous stem cell transplantation following CML cell purging are examples of important approaches to improving CML treatment. Received: 22 June 1998 / Accepted: 28 August 1998     

Management of chronic myeloid leukemia presenting with isolated thrombocytosis and complex Philadelphia chromosome: A case report

Rationale:Chronic myelogenous leukemia (CML) with thrombocytosis and complex chromosomal translocation is extremely rare in clinical setting. Here, we reported the clinical and pathological characteristics of CML patients, which were characterized by thrombocytosis and complex Philadelphia chromosome translocation. Moreover, we also introduced our therapeutic schedule for this patient as well as review relative literature.Patient concerns:A 24-year-old female presented with night sweating, fatigue, and intermittent fever for 1 month.Diagnosis:Fluorescence in situ hybridization results revealed that breakpoint cluster region (BCR)-Abelson (ABL) gene fusion in 62% of the cells and karyotyping showed a complex 3-way 46, XY, t(9;22;11) (q34;q11;q13) [19/20] translocation. This patient was diagnosed with CML complicated with thrombocytosis and complex Philadelphia chromosome translocation.Interventions:The patients received continuously oral imatinib mesylate tablets (400 mg) once a day.Outcomes:After treatment with imatinib for 3 months, the BCR/ABL^IS was less than 0.1% and achieved major molecular response. Moreover, the BCR/ABL^IS of this patient achieved major molecular response. The BCR/ABL^IS values at 6 months and 12 months were less than 0.01% and 0.0032%, respectively. And no BCR/ABL fusion was detected in the next 2 years follow-up period.Lessons:Imatinib might represent a preferred therapeutic option for CML patients with rare thrombocytosis and complex chromosomal translocation. In addition, BCR/ABL fusion gene examination in patients with thrombocytosis might represent an effective strategy to avoid the misdiagnosis of this specific CML population.     

Chronic myeloid leukemia: 2012 update on diagnosis,monitoring, and management

Disease overview:

Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm with an incidence of one–two cases per 100,000 adults and accounts for ～15% of newly diagnosed cases of leukemia in adults.

Diagnosis:

CML is characterized by a balanced genetic translocation, t(9;22)(q34;q11.2), involving a fusion of the Abelson oncogene (ABL) from chromosome 9q34 with the breakpoint cluster region (BCR) gene on chromosome 22q11.2. This rearrangement is known as the Philadelphia chromosome. The molecular consequence of this translocation is the generation of a BCR‐ABL fusion oncogene, which in turn translates into a Bcr‐Abl oncoprotein.

Frontline therapy:

Three tyrosine kinase inhibitors (TKIs), imatinib, nilotinib, and dasatinib, have been approved by the US Food and Drug Administration for the first‐line treatment of patients with newly diagnosed CML in chronic phase (CML‐CP). Clinical trials with 2nd generation TKIs reported significantly deeper and faster responses; their impact on long‐term survival remains to be determined.

Salvage therapy:

For patients who fail standard‐dose imatinib therapy, imatinib dose escalation is a second‐line option. Alternative second‐line options include 2nd generation TKIs. Although both are potent and specific BCR‐ABL TKIs, dasatinib and nilotinib exhibit unique pharmacological profiles and response patterns relative to different patient characteristics, such as disease stage and BCR‐ABL mutational status. Patients who develop the T315I “gatekeeper” mutation display resistance to all currently available TKIs and are candidate for clinical trials. Allogeneic transplantation remains an important therapeutic option for CML‐CP harboring the T315I mutation, patients who fail 2nd generation TKIs, and for all patients in advanced phase disease. Am. J. Hematol., 2012. © 2012 Wiley Periodicals, Inc.     

p185(BCR/ABL) has a lower sensitivity than p210(BCR/ABL) to the allosteric inhibitor GNF-2 in Philadelphia chromosome-positive acute lymphatic leukemia

Background

The t(9;22) translocation leads to the formation of the chimeric breakpoint cluster region/c-abl oncogene 1 (BCR/ABL) fusion gene on der22, the Philadelphia chromosome. The p185^BCR/ABL or the p210^BCR/ABL fusion proteins are encoded as a result of the translocation, depending on whether a “minor” or “major” breakpoint occurs, respectively. Both p185^BCR/ABL and p210^BCR/ABL exhibit constitutively activated ABL kinase activity. Through fusion to BCR the ABL kinase in p185^BCR/ABL and p210^BCR/ABL “escapes” the auto-inhibition mechanisms of c-ABL, such as allosteric inhibition. A novel class of compounds including GNF-2 restores allosteric inhibition of the kinase activity and the transformation potential of BCR/ABL. Here we investigated whether there are differences between p185^BCR/ABL and p210^BCR/ABL regarding their sensitivity towards allosteric inhibition by GNF-2 in models of Philadelphia chromosome-positive acute lymphatic leukemia.

Design and Methods

We investigated the anti-proliferative activity of GNF-2 in different Philadelphia chromosome-positive acute lymphatic leukemia models, such as cell lines, patient-derived long-term cultures and factor-dependent lymphatic Ba/F3 cells expressing either p185^BCR/ABL or p210^BCR/ABL and their resistance mutants.

Results

The inhibitory effects of GNF-2 differed constantly between p185^BCR/ABL and p210^BCR/ABL expressing cells. In all three Philadelphia chromosome-positive acute lymphatic leukemia models, p210^BCR/ABL-transformed cells were more sensitive to GNF-2 than were p185BCR/ABL-positive cells. Similar results were obtained for p185^BCR/ABL and the p210^BCR/ABL harboring resistance mutations.

Conclusions

Our data provide the first evidence of a differential response of p185^BCR/ABL- and p210^BCR/ABL- transformed cells to allosteric inhibition by GNF-2, which is of importance for the treatment of patients with Philadelphia chromosome-positive acute lymphatic leukemia.     

Current paradigms in the management of Philadelphia chromosome positive acute lymphoblastic leukemia in adults

Philadelphia chromosome‐positive (Ph‐positive) acute lymphoblastic leukemia (ALL) is a biologically, clinically, and genetically distinct subtype of precursor‐B ALL. The Ph chromosome, results from a reciprocal translocation of the ABL1 kinase gene on chromosome 9 to the breakpoint cluster region (BCR) gene on chromosome 22. Depending on the translocation breakpoint, typically a p210 BCR‐ABL1 or a p190 BCR‐ABL onc protein are generated; both are constitutively active tyrosine kinases that play a central role to alter signaling pathways of cell proliferation, survival, and self‐renewal, leading to leukemogenesis. In Ph‐positive ALL, the p190‐BCR‐ABL (minor [m]‐bcr) subtype is more frequent than the p210‐BCR‐ABL (major [M]‐bcr) subtype, commonly found in chronic myeloid leukemia. The Philadelphia chromosome is the most frequent recurrent cytogenetic abnormality in elderly patients with ALL. Its incidence increases with age, reaching ～50% in patients with ALL aged 60 years and over. Patients traditionally had a very poor outcome with chemotherapy, particularly if they do not undergo allogeneic hematopoietic cell transplantation (allo‐HCT) in first complete remission (CR1). With the availability of multiple tyrosine kinase inhibitors (TKI), the therapeutic armamentarium is expanding quickly. However, there is no consensus on how to best treat Ph‐positive ALL. With modern therapy, improved outcomes have led to the emergence of a number of controversies, including the need for intensive chemotherapy, the ideal TKI, and whether all eligible patients should receive an allo‐HSCT, and if so, what type. Here, we discuss these controversies in light of the available literature.     

Complex chromosome rearrangements may locate the bcr/abl fusion gene sites other than 22q11

BACKGROUND AND OBJECTIVE: From 5-8% of Philadelphia (Ph) positive patients with chronic myeloid leukemia (CML) show variant translocations in which at least a third chromosome in addition to 9q34 and 22q11 is involved. The formation mechanisms and clinical significance of variant Ph translocations are still unclear. The BCR/ABL chimeric gene encoding for chimeric proteins is always present and maps on the 22q- regardless of the type of translocation. We studied two apparently Ph negative CML patients with unusual karyotypes both showing a typical b3a2 rearrangement. DESIGN AND METHODS: Dual-color fluorescence in situ hybridization (FISH) can visualize BCR and ABL genes and localize the BCR/ABL fusion gene. We used FISH to study the formation mechanisms of variant Ph translocations in two patients. RESULTS: The chimeric BCR/ABL gene was located on a locus other than the expected 22q11 in both patients. In the first case the fusion signal was present on the 9q34 band whereas in the second patient it was detected on chromosome 8, involved in masked Ph formation. INTERPRETATION AND CONCLUSIONS: The location of the hybrid BCR/ABL gene on chromosomes other than 22q- is a rare event which can only be observed using the FISH technique. When these unusual translocations occur the hypothesis most often put forward is that several consecutive cytogenetic events have taken place. The factors which regulate the formation of these breakpoints have yet to be clarified. The FISH technique allows the identification of chromosome rearrangements that could not otherwise be detected by conventional banding procedures. The location of the hybrid BCR/ABL gene on sites other than 22q11 represents a rare type of variant Ph translocation.The real frequency and clinical significance of such rearrangements need to be investigated.     

Chronic myeloid leukemia: 2014 update on diagnosis,monitoring, and management

Disease overview : Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm with an incidence of 1–2 cases per 100,000 adults, and accounts for ～15% of newly diagnosed cases of leukemia in adults. Diagnosis : CML is characterized by a balanced genetic translocation, t(9;22)(q34;q11.2), involving a fusion of the Abelson oncogene (ABL) from chromosome 9q34 with the breakpoint cluster region (BCR) gene on chromosome 22q11.2. This rearrangement is known as the Philadelphia chromosome. The molecular consequence of this translocation is the generation of a BCR‐ABL fusion oncogene, which in turn translates into a Bcr‐Abl oncoprotein. Frontline therapy : Three tyrosine kinase inhibitors (TKIs), imatinib, nilotinib, and dasatinib have been approved by the US Food and Drug Administration for the first‐line treatment of patients with newly diagnosed CML in chronic phase (CML‐CP). Clinical trials with second generation TKIs reported significantly deeper and faster responses; their impact on long‐term survival remains to be determined. Salvage therapy : For patients who fail frontline therapy, second‐line options include second and third generation TKIs. Although second and third generation TKIs are potent and specific BCR‐ABL TKIs, they exhibit unique pharmacological profiles and response patterns relative to different patient characteristics, such as patients comorbidities, disease stage, and BCR‐ABL mutational status. Patients who develop the T315I “gatekeeper” mutation display resistance to all currently available TKIs except ponatinib. Allogeneic transplantation remains an important therapeutic option for CML‐CP who have failed at least 2 TKIs, and for all patients in advanced phase disease. Am. J. Hematol. 89:547–556, 2014. © 2014 Wiley Periodicals, Inc.     

Phase II trial of HyperCVAD and Dasatinib in patients with relapsed Philadelphia chromosome positive acute lymphoblastic leukemia or blast phase chronic myeloid leukemia

Dasatinib is a second generation tyrosine kinase inhibitor, with activity in imatinib resistant Ph‐positive ALL. We have treated 34 patients with relapsed Philadelphia chromosome positive acute lymphoblastic leukemia (ALL) (n = 19) or lymphoid blast phase of chronic myelogenous leukemia (CML‐LB) (n = 15) with the combination of dasatinib and the hyperCVAD regimen. Prior regimens included hyperCVAD plus imatinib (n = 11, 4 had transplant in first CR), other combination chemotherapy (n = 12), monotherapy with kinase inhibitors other than dasatinib (n = 9), and investigational agents (n = 2). Pretreatment ABL mutations were noted in 10 patients. The overall response rate was 91%, with 24 patients (71%) achieving complete response (CR), and 7(21%) CR with incomplete platelet recovery (CRp). Two patients died during induction and one had progressive disease. Twenty‐six patients (84%) achieved complete cytogenetic remission after one cycle of therapy. Overall, 13 patients (42%) achieved complete molecular response, and 11 patients (35%) had major molecular response (BCR‐ABL/ABL<0.1%). Nine patients proceeded to allogeneic transplantation. Grades 3 and 4 toxicities included hemorrhage, pleural and pericardial effusions and infections. The median follow‐up for patients with CML‐LB is 37.5 months (range, 7–70 months) with a 3‐year overall survival of 70%; 68% remained in CR at 3 years. For ALL patients, the median follow‐up is 52 months (range, 45–59 months) with a 3‐year survival of 26%; 30% remain in CR at 3 years. The combination of HyperCVAD regimen with dasatinib is effective in patients with relapsed Ph‐positive ALL and CML‐LB. Am. J. Hematol. 89:282–287, 2014. © 2013 Wiley Periodicals, Inc.     

Uncommon case of chronic myeloid leukemia with multiple myeloma

We describe a 72-year-old woman who was diagnosed with asymptomatic multiple myeloma (MM) while being treated for Philadelphia (Ph)-positive chronic myeloid leukemia (CML) with imatinib mesylate (400 mg/day). The diagnosis of CML was based on the presence of the Ph chromosome and chimeric BCR-ABL messenger RNA. Three months after starting imatinib mesylate treatment, the patient achieved a complete cytogenetic response. However, bone marrow analysis at that time demonstrated plasmacytosis, and paraprotein (IgG, κ-type) was also detected. Hypercalcemia, renal failure, anemia, and bone lesions were not observed, which suggested that asymptomatic MM had developed. The coexistence of CML and MM is an extremely uncommon event that has only been reported in 12 cases. We discuss the relationship between CML and MM.     

Chronic myeloid leukemia: 2016 update on diagnosis,therapy, and monitoring

Disease overview: Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm with an incidence of 1‐2 cases per 100,000 adults. It accounts for approximately 15% of newly diagnosed cases of leukemia in adults. Diagnosis: CML is characterized by a balanced genetic translocation, t(9;22)(q34;q11.2), involving a fusion of the Abelson gene (ABL1) from chromosome 9q34 with the breakpoint cluster region (BCR) gene on chromosome 22q11.2. This rearrangement is known as the Philadelphia chromosome. The molecular consequence of this translocation is the generation of a BCR‐ABL1 fusion oncogene, which in turn translates into a BCR‐ABL oncoprotein. Frontline therapy: Three tyrosine kinase inhibitors (TKIs), imatinib, nilotinib, and dasatinib are approved by the United States Food and Drug Administration for first‐line treatment of patients with newly diagnosed CML in chronic phase (CML‐CP). Clinical trials with 2nd generation TKIs reported significantly deeper and faster responses; their impact on long‐term survival remains to be determined. Salvage therapy: For patients who fail frontline therapy, second‐line options include second and third generation TKIs. Although second and third generation TKIs are potent and selective TKIs, they exhibit unique pharmacological profiles and response patterns relative to different patient and disease characteristics, such as patients’ comorbidities, disease stage, and BCR‐ABL1 mutational status. Patients who develop the T315I “gatekeeper” mutation display resistance to all currently available TKIs except ponatinib. Allogeneic stem cell transplantation remains an important therapeutic option for patients with CML‐CP who have failed at least two TKIs, and for all patients in advanced phase disease. Am. J. Hematol. 91:253–265, 2016. © 2015 Wiley Periodicals, Inc.     

The differences and correlations of BCR‐ABL transcripts between peripheral blood and bone marrow assays are associated with the molecular responses in the bone marrow for chronic myelogenous leukemia

Previous studies concerning BCR‐ABL mRNA levels by quantitative real‐time RT‐PCR (Q‐PCR) for chronic myelogenous leukemia (CML) have shown a significant concordance between peripheral blood (PB) and bone marrow (BM) assays. The objective of this study was to determine whether molecular monitoring using PB was comparable to using BM for CML. A comparative study was performed that analyzed the Q‐PCR results of 712 simultaneous PB and BM samples from 330 patients before and during imatinib therapy. For the 78 paired pretreatment samples, the level of BCR‐ABL mRNA in PB was lower than that in BM (P = 0.007). Although the overall amounts of BCR‐ABL mRNA in the PB and BM were comparable (P= 0.072) and there was a strong correlation (r = 0.839, P < 0.001) with the 634 paired on‐treatment samples, the depth of the molecular response in PB was lower than that in BM (P < 0.001). The level of BCR‐ABL mRNA in PB was lower than that in BM where the BM BCR‐ABL mRNA < 1 log reduction (P < 0.001) or ≥ 1–< 2 log‐reductions (P = 0.008) from the baseline, and higher than that where the BM BCR‐ABL mRNA ≥ 2 log‐reductions (P < 0.001). A strong correlation (r = 0.811, P < 0.001) was only found where the BM BCR‐ABL mRNA < 1 log reduction. We conclude that the differences and correlations of BCR‐ABL mRNA between PB and BM assays depend on the depth of the molecular response in BM for CML during imatinib therapy. Am. J. Hematol., 2012. © 2012 Wiley Periodicals, Inc.     

Localization of the human c-sis oncogene in Ph1-positive and Ph1-negative chronic myelocytic leukemia by in situ hybridization

Oncogenes are a group of evolutionary conserved cellular genes (c-onc) homologous to the transforming genes of oncogenic retroviruses (v-onc). Some of them are localized near the breakpoints of specific chromosomal aberrations occurring in various neoplasms, as for example the Philadelphia translocation, t(9;22)(q34;q11), in chronic myelocytic leukemia (CML). Recently, we localized the human c-abl oncogene to chromosome region 9q34 and demonstrated a translocation of this gene to the Philadelphia chromosome (Ph1,22q-) in various forms of Ph1-positive, but not Ph1-negative, chronic myelocytic leukemia (CML). Another human oncogene, c-sis, is located on chromosome 22 and was recently reported to be transferred to chromosome 9q+ in one CML patient. We have now studied 2 CML patients with classic and variant types of Ph1 translocation, one Ph1-negative case, and a healthy control using in situ hybridization of a c-sis probe to metaphase chromosomes. These studies show that c-sis: (1) is localized to region 22q12.3-q13.1, far away from the breakpoint region 22q11 in CML, (2) segregates with the translocated part of chromosome 22 to different chromosomes in Ph1-positive patients, and (3) remains on chromosome 22 in the Ph1-negative case. Therefore, these data give no support for an active role of the c-sis gene in the generation of CML. Thus, if either of these two oncogenes is involved in the development of Ph1-positive CML, c-abl appears to be the more important one.     

Chromosome 3q21 abnormalities associated with hyperactive thrombopoiesis in acute blastic transformation of chronic myeloid leukemia

Two patients with acute blastic transformation of chronic myeloid leukemia (CML) associated with strikingly elevated platelet counts showed abnormalities of chromosome 3q in addition to the standard Philadelphia (Ph1) chromosome translocation. The first patient had an inversion of chromosome 3 (q21q26) cytologically identical to an inversion 3 previously reported in de novo acute megakaryoblastic leukemia, and the second patient showed a translocation between chromosome 3q and the chromosome 9 homologue not involved in the Ph1 translocation, [t(3;9)(q21;q34)]. Previous studies had incriminated either 3q21 or 3q26 as the locus for a regulatory thrombopoietic gene, but the current study suggests that 3q21 is the relevant site.     

High reliability and sensitivity of the BCR/ABL1 D-FISH test for the detection of BCR/ABL rearrangements

The BCR/ABL1 fusion gene is mainly caused by the t(9; 22)(q34; q11.2) translocation, which results in the Philadelphia (Ph) chromosome. The Ph chromosome is the typical hallmark in chronic myeloid leukemia (CML), but can also be present in acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The BCR/ABL1 rearrangement is an important tumor classification marker and a useful prognostic factor allowing an adequate therapy management. Ph chromosome detection by conventional cytogenetics (CC) can be hampered by low quantity and quality of metaphases from tumor cells. Furthermore, BCR/ABL1 rearrangements may be hidden due to cryptic rearrangements or complex aberrations. Therefore, molecular cytogenetic methods turned out to be useful tools for the detection of BCR/ABL1 rearrangements. We performed fluorescent in situ hybridization (FISH) with the recently developed BCR/ABL1 D-FISH probe (QBIOgene, Illkirch, F) on cultured bone marrow and peripheral blood cells of 71 patients with CML, ALL, AML, and myeloproliferative disorder (MPD). FISH results and the results of banding methods were directly compared. Based on the analyses of >200 nuclei per patient, D-FISH correlated closely with CC and allowed an accurate quantification of BCR/ABL1 rearrangements even in a low percentage of aberrant cells. No false-positive or false-negative results were obtained. Furthermore, the D-FISH probe detected three cryptic and one complex BCR/ABL1 rearrangement, which were not visible by CC. We conclude that D-FISH reliably detects standard Ph chromosomes as well as its variant translocations and accurately quantifies BCR/ABL1 rearrangements prior and during cancer treatment as well as in the phase of remission, in daily routine tumor cytogenetic diagnostics.