The Philadelphia chromosome. Considerations based on studies of variant Ph translocations

A Novel Four-Way Complex Variant Translocation Involving Chromosome 46,XY,t(4;9;19;22)(q25:q34;p13.3;q11.2) in a Chronic Myeloid Leukemia Patient

Philadelphia (Ph) chromosome (9;22)(q34;q11) is well established in more than 90% of chronic myeloid leukemia (CML) patients, and the remaining 5-8% of CML patients show variant and complex translocations, with the involvement of third, fourth, or fifth chromosome other than 9;22. However, in very rare cases, the fourth chromosome is involved. Here, we found a novel case of four-way Ph+ chromosome translocation involving 46,XY,t(4;9;19;22)(q25:q34;p13.3;q11.2) with CML in the chronic phase. Complete blood cell count of the CML patient was carried out to obtain total leukocytes count, hemoglobin, and platelets. Fluorescence in situ hybridization technique was used for the identification of BCR-ABL fusion gene, and cytogenetic test for the confirmation of Ph (9;22)(q34;q11) and the mechanism of variant translocation in the bone marrow. The patient is successfully treated with a dose of 400 mg/day imatinib mesylate (Gleevec). We observed a significant decrease in white blood cell count of 11.7 × 10(9)/L after 48-month follow-up. Patient started feeling better generally. There was a reduction in the swelling of the body, fatigue, and anxiety.

Cytogenetic and Molecular Analyses of Philadelphia Chromosome Variants in CML (chronic myeloid leukemia) Patients from Sindh using Karyotyping and RT-PCR

Objective:

To determine the frequency of Philadelphia chromosome (Ph) and its variants in chronic myeloid leukemia (CML) cases at a tertiary care hospital of Sindh.

Methods:

The study was conducted at the Department of Pathology, Liaquat University of Medical and Health Sciences, Jamshoro and Isra University Hospital, Hyderabad during May-to-September 2014. Bone marrow and peripheral blood samples from a total of 145 diagnosed cases of CML were collected. Cytogenetic analyses were performed using karyotyping as per the International System for Human Cytogenetic Nomenclature guidelines. All karyotypic images were analyzed using the Cytovision software. In order to identify BCR-ABL transcripts, RT-PCR was performed. Statistical analysis of the data was done using SPSS-version-21.0.

Results:

Of the 145 samples, a total of 133 (91.7%) were positive for the Ph (Ph+) while 12 (8.3%) were negative for the Ph (Ph-). Of the 133 Ph+ samples, standard karyotypes were noted in 121 (91%), simple variants in 9 (6.7%) and complex variants in 3 (2.3%) of the samples. All the Ph+ samples (n=133) showed BCR-ABL positivity. Of the 12 Ph- samples, a total of 7 (58.3%) were BCR-ABL-positive and 5 (41.6%) were BCR-ABL-negative.

Conclusion:

Frequency of the Ph was found to be of 90.9% in CML patients using a highly sensitive technique, the RT-PCR. Cytogenetic abnormalities were at a lower frequency. Cytogenetic and molecular studies must be conducted for better management of CML cases. These findings could be very useful in guiding the appropriate therapeutic options for CML patients.

Diversity of breakpoints of variant Philadelphia chromosomes in chronic myeloid leukemia in Brazilian patients

BACKGROUND

Chronic myeloid leukemia is a myeloproliferative disorder characterized by the Philadelphia chromosome or t(9;22)(q34.1;q11.2), resulting in the break-point cluster region-Abelson tyrosine kinase fusion gene, which encodes a constitutively active tyrosine kinase protein. The Philadelphia chromosome is detected by karyotyping in around 90% of chronic myeloid leukemia patients, but 5-10% may have variant types. Variant Philadelphia chromosomes are characterized by the involvement of another chromosome in addition to chromosome 9 or 22. It can be a simple type of variant when one other chromosome is involved, or complex, in which two or more chromosomes take part in the translocation. Few studies have reported the incidence of variant Philadelphia chromosomes or the breakpoints involved among Brazilian chronic myeloid leukemia patients.

OBJECTIVE

The aim of this report is to describe the diversity of the variant Philadelphia chromosomes found and highlight some interesting breakpoint candidates for further studies.

METHODS

the Cytogenetics Section Database was searched for all cases with diagnoses of chronic myeloid leukemia during a 12-year period and all the variant Philadelphia chromosomes were listed.

RESULTS

Fifty (5.17%) cases out of 1071 Philadelphia-positive chronic myeloid leukemia were variants. The most frequently involved chromosome was 17, followed by chromosomes: 1, 20, 6, 11, 2, 10, 12 and 15.

CONCLUSION

Among all the breakpoints seen in this survey, six had previously been described: 11p15, 14q32, 15q11.2, 16p13.1, 17p13 and 17q21. The fact that some regions get more frequently involved in such rare rearrangements calls attention to possible predisposition that should be further studied. Nevertheless, the pathological implication of these variants remains unclear.

[Particular evolution of complex cytogenetic variants of chronic myeloid leukemia treated with imatinib]

Les variants cytogénétiques simples et complexes constituent 5 à 10% de tous les cas de leucémie myéloïde chronique. Le mécanisme de leur formation a été proposé par certains auteurs. Les aspects clinique, thérapeutique et pronostique ne sont pas différents des formes classiques à l'aire des anti-tyrosines kinases. Nous rapportons deux cas traités par Imatinib dont l'évolution cytogénétique a été particulière. Les deux patients ont été inclus dans le programme GIPAP après signature d'un consentement éclairé. Chaque patient a bénéficié d'un examen clinique, d'un hémogramme, d'un myélogramme, d'un caryotype et ou d'une hybridation intra-génique avec fluorescence avant inclusion dans le programme. Chaque patient après inclusion a été traité avec l'Imatinib à la dose quotidienne de 400mg. La surveillance clinique, hématologique et cytogénétique et moléculaire a été faite selon les recommandations de LeukemiaNet.

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.

A Rare t(9;22;16)(q34;q11;q24) Translocation in Chronic Myeloid Leukemia for Which Imatinib Mesylate Was Effective: A Case Report

The t(9;22)(q34;q11) translocation is found in about 90% of chronic myeloid leukemia (CML) patients. About 5-10% of CML patients have complex variant translocations involving a third chromosome in addition to chromosomes 9 and 22. Herein, we describe a CML-chronic phase male with a complex translocation involving chromosome 16, t(9;22;16)(q34;q11;q24). First, he was treated with interferon-alpha and intermittent hydroxyurea, but only a partial cytogenetic response was attained. Subsequently, the patient was treated with imatinib mesylate because of an additional chromosome abnormality, trisomy 8. A major molecular response was obtained after one year's imatinib therapy, and the follow-up chromosomal analysis performed 4 years and 3 months after the initiation of imatinib therapy displayed a normal karyotype of 46,XY.

New complex chromosomal translocation in chronic myeloid leukaemia: t(9;18;22)(q34;p11;q11)

A Chronic myeloid leukaemia (CML) case with a new complex t(9;18;22)(q34;p11;q11) of a 29-year-old man is being reported. For the first time, this translocation has been characterized by karyotype complemented with fluorescence in situ hybridization (FISH). In CML, the complex and standard translocations have the same prognosis. The patient was treated with standard initial therapy based on hydroxyurea before he died due to heart failure four months later. Our finding indicates the importance of combined cytogenetic analysis for diagnosis and guidance of treatment in clinical diagnosis of CML.

On the genesis and prognosis of variant translocations in chronic myeloid leukemia

Variant translocations involving 9q, 22q, and at least one additional genomic locus occur in 5-10% of patients with chronic myeloid leukemia (CML). The mechanisms for the formation of these variant translocations are not fully characterized. Studies on the prognosis of these variant translocations revealed conflicting results. In addition, deletions in the derivative chromosome 9 are reportedly more frequent among variant translocation cases. We analyzed cytogenetic and FISH data from 22 CML patients with variant translocations tested at our laboratory. Deletions were observed in 6 of the 14 cases with FISH data available (43%), consistent with the literature and higher than in typical translocation cases (12-15%). Sequential changes of 9q deletions are possible and could be acquired as the disease progresses in addition to simultaneous formation of the Philadelphia chromosome with the deletion. Variant translocation CML patients with a deletion showed a worse cytogenetic response 1 year after therapy than those without a deletion (P < 0.05). Variant translocations may be formed by either a one-step or a two-step mechanism. Proper assessment of the prognostic significance of variant translocations requires better categorization of these translocations based on their mechanisms of genesis and the deletion status.

Jumping translocation of 17q11∼qter and 3q25∼q28 duplication in a variant Philadelphia t(9;14;22)(q34;q32;q11) in a childhood chronic myelogenous leukemia

The virtually obligatory presence of the Philadelphia chromosome may suggest a causal homogeneity, but chronic myelogenous leukemia (CML) is a clinically heterogeneous disease. This may be a consequence of the variable BCR breakpoints on chromosome 22 and of nonrandom secondary chromosomal abnormalities. We present the case of a boy, age 12, investigated in blastic phase of CML. Karyotyping with conventional and multiplex fluorescence in situ hybridization (FISH and M-FISH) karyotyping, complemented with reverse transcriptase-polymerase chain reaction, identified a variant Philadelphia translocation t(9;14;22)(q34;q32;q11) involving a cryptic BCR/ABL fusion with formation of the p190(Bcr-Abl) oncoprotein. M-FISH revealed also an unbalanced jumping translocation of 17q11 approximately qter alternatively present on chromosomes 14 or 20, apparently hithertofore unreported in hematological malignancies. Another secondary aberration, dup(3)(q25q28), was revealed by multipoint interphase FISH (mpI-FISH). Gain of this region is known in adult hematological malignancies and solid tumors, suggesting its general involvement in tumor initiation or progression (or both), regardless of tissue origin.

t(14;22)(q32;q11) in non-Hodgkin lymphoma and myeloid leukaemia: molecular cytogenetic investigations

Two non-Hodgkin lymphomas (NHL), one chronic lymphocytic leukaemia/small lymphocytic lymphoma and one diffuse large B-cell lymphoma and three cases of myeloid leukaemia, two chronic (CML) and one acute (AML), showed, by G-banding analysis, apparently identical chromosomal translocations t(14;22)(q32;q11), in three of the cases as the sole abnormality. Fluorescence in situ hybridisation (FISH) analysis with locus-specific probes for ABL at 9q34 [bacterial artificial chromosomes (BACs) 835J22 and 1132H12], IGH at 14q32 [P1 artificial chromosome (PAC) 998D24] and IGL (PAC 1019H10) and BCR (BAC 74M14) at 22q11, as well as multicolour in situ hybridisation (M-FISH) analyses were performed. A three-way variant translocation of the classical t(9;22)(q34;q11), t(9;22;14)(q34;q11;q32), involving both BCR and ABL, was unravelled by the molecular cytogenetic investigations in the three myeloid leukaemia cases; a similar variant translocation has previously been reported in seven CML. The two cases of NHL (one NHL with a similar 14;22-translocation has been reported previously) had no involvement of BCR or ABL, but instead the IGH and IGL genes were shown to be juxtaposed by the t(14;22)(q32;q11). How such a rearrangement with recombination of IGH and IGL might elicit a pathogenetic effect is completely unknown.

A complex translocation (9;22;16)(q34;q11.2;p13) in chronic myelocytic leukemia

The t(9;22) is present in almost all cases with chronic myelocytic leukemia (CML). Around 5% of these patients show complex translocations involving a third chromosome in addition to chromosomes 9 and 22. All chromosomes have participated in these variants and the BCR-ABL1 hybrid gene is always present. We describe a CML case with a new complex t(9;22;16)(q34;q11.2;p13). Seven months after imatinib treatment a karyotype showed the appearance of a clone with a standard t(9;22) in addition to the clone with the complex translocation. The b3a2 transcript of BCR-ABL1 was detected both at diagnosis and 7 months after therapy. In CML, both complex translocations and standard translocations have the same prognosis. However, these complex variants could contribute to the tumoral evolution by conferring selective advantages that, in turn, cause the preferential manifestation at diagnosis of clones with complex translocations.

Breakpoints of variant 9;22 translocations in chronic myeloid leukemia locate preferentially in the CG-richest regions of the genome

From 5% to 10% of 9;22 translocations in chronic myeloid leukemia (CML) are reported to occur in variant form, that is, with the involvement of other regions of the genome in 3-way or more rearrangements. The literature indicates that the alternative breakpoints are not distributed randomly in the genome but show hotspots. We present data on 289 unpublished cases of CML with variant 9;22 translocations having a total of 342 variant breakpoints, the largest independent series to date. We found that the distribution of breaks was in loose agreement with the literature but that some new hotspots were identified; furthermore, some published hotspots were not fully supported by our data. Moreover, when our 342 variant breakpoints were plotted against profiles of CG heterogeneity in the genome, a significant positive correlation between breakpoint locations and CG composition was observed. In an ancillary study, we compared the frequency of variant t(9;22) with that of variants of t(15;17) associated with acute promyelocytic leukemia (AML M3). We found that the frequency of the former, 9.3%, was significantly higher than that of the latter, 2.6%.

Natural history and staging of chronic myelogenous leukemia

The natural history of chronic myelogenous leukemia (CML) has changed in recent years, partly due to earlier diagnosis but mostly as a consequence of the availability of effective therapies that have the potential to eradicate the Philadelphia chromosome-positive clone. Highly effective therapy with imatinib has changed the prognostic significance of clinical features traditionally associated with poor outcome. Achieving a complete cytogenetic response and a major molecular response early during the course of therapy with imatinib may be the most important factor in determining longterm outcome. Therefore, treatment modalities that increase the probability of achieving this goal should be pursued. This article describes the natural history of CML and its prognostic factors,with emphasis on changes due to the emergence of imatinib.

Results of imatinib mesylate therapy in chronic myelogenous leukaemia with variant Philadelphia chromosome

Five to 10 per cent of patients with Philadelphia chromosome (Ph)-positive chronic myelogenous leukaemia (CML) have variant translocations involving chromosomes other than 9 and 22. We investigated the characteristics and outcome of patients with variant translocations treated with imatinib. Among 721 patients, 44 (6%) had variant translocations, involving one (n = 39) or two (n = 4) additional chromosomes. Nineteen patients (44%) were in chronic (12 previously untreated), 24 (55%) in accelerated and one (2%) in blastic phase. A major cytogenetic response was achieved in 14 (74%) patients treated in chronic phase and in 14 (58%) treated in accelerated phase. Six of 13 (46%) evaluable patients had deletion of derivative chromosome 9, and there was a trend for a lower response rate in these patients. We compared the 43 patients in chronic or accelerated phase to 678 patients with classic Ph treated with imatinib. The only significant difference in clinical characteristics was a higher frequency of accelerated phase among those with variant translocations (56%) compared with those with classic translocations (38%). No differences in outcome were evident. In a multivariate analysis, variant Ph translocations had no impact in response rate, overall survival or duration of response. We conclude that patients with variant Ph translocations have a similar prognosis to those with classic Ph translocations when treated with imatinib.

Genesis of variant philadelphia chromosome translocations in chronic myelocytic leukemia

The Philadelphia (Ph) chromosome is found in more than 90% of chronic myelocytic leukemia (CML) patients. In most cases, it results from the reciprocal t(9;22)(q34;q11), with the ABL proto-oncogene from 9q34 fused to the breakpoint cluster region (BCR) locus on 22q11. In 5%-10% of patients with CML, the Ph chromosome originates from variant translocations, involving various breakpoints in addition to 9q34 and 22q11. In our investigation, three CML cases with complex Ph translocations have been analyzed by G-banding and fluorescence in situ hybridization (FISH). FISH with breakpoint-spanning probes for the BCR and ABL genes revealed information about the genesis of complex Ph translocations. The occurrence of one fusion signal indicates a one-step mechanism (case 1). Two fusion signals indicate a two-step mechanism (case 2). Lack of signals indicates deletions of parts of the BCR and ABL genes or of adjacent regions (case 3).

Survival implications of molecular heterogeneity in variant Philadelphia-positive chronic myeloid leukaemia

The BCR-ABL fusion in chronic myeloid leukaemia (CML) is generated by the Philadelphia (Ph) translocation t(9;22) or, in 10% of patients, variants thereof (vPh). Deletion encompassing the reciprocal product (ABL-BCR) from the derivative chromosome 9 [der(9)] occurs in 15% of all patients, but with greater frequency in vPh patients. Reports of physical separation of ABL-BCR in non-deleted patients, as well as evolution from classical to variant Ph, introduce further heterogeneity to the vPh subgroup and raise the possibility that such translocations may herald disease progression. Survival analyses, however, have thus far yielded contradictory results. We assessed the frequency of der(9) deletions, ABL-BCR abrogation, cytogenetic evolution and cryptic rearrangement in a large cohort of 54 patients with vPh CML. Deletions encompassing ABL-BCR were detected in 37% of patients, consistent with a model in which a greater number of chromosome breaks increases the risk of genomic loss. The components of ABL-BCR were physically separated in a further 52% of patients while fused in the remaining 11%. Evolution from classical to vPh was demonstrated in three patients. The difference in survival, as indicated by Kaplan-Meier analysis, was marked between classical and vPh patients (105 vs 60 months respectively; P = 0.0002). Importantly, this difference disappeared when patients with deletions were removed from the analysis. Our study showed that, despite the existence of several levels of genomic heterogeneity in variant Ph-positive CML, der(9) deletion status is the key prognostic factor.

Cytogenetic and molecular genetic evolution of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is genetically characterized by the presence of the reciprocal translocation t(9;22)(q34;q11), resulting in a BCR/ABL gene fusion on the derivative chromosome 22 called the Philadelphia (Ph) chromosome. In 2-10% of the cases, this chimeric gene is generated by variant rearrangements, involving 9q34, 22q11, and one or several other genomic regions. All chromosomes have been described as participating in these variants, but there is a marked breakpoint clustering to chromosome bands 1p36, 3p21, 5q13, 6p21, 9q22, 11q13, 12p13, 17p13, 17q21, 17q25, 19q13, 21q22, 22q12, and 22q13. Despite their genetically complex nature, available data indicate that variant rearrangements do not confer any specific phenotypic or prognostic impact as compared to CML with a standard Ph chromosome. In most instances, the t(9;22), or a variant thereof, is the sole chromosomal anomaly during the chronic phase (CP) of the disease, whereas additional genetic changes are demonstrable in 60-80% of cases in blast crisis (BC). The secondary chromosomal aberrations are clearly nonrandom, with the most common chromosomal abnormalities being +8 (34% of cases with additional changes), +Ph (30%), i(17q) (20%), +19 (13%), -Y (8% of males), +21 (7%), +17 (5%), and monosomy 7 (5%). We suggest that all these aberrations, occurring in >5% of CML with secondary changes, should be denoted major route abnormalities. Chromosome segments often involved in structural rearrangements include 1q, 3q21, 3q26, 7p, 9p, 11q23, 12p13, 13q11-14, 17p11, 17q10, 21q22, and 22q10. No clear-cut differences as regards type and prevalence of additional aberrations seem to exist between CML with standard t(9;22) and CML with variants, except for slightly lower frequencies of the most common changes in the latter group. The temporal order of the secondary changes varies, but the preferred pathway appears to start with i(17q), followed by +8 and +Ph, and then +19. Molecular genetic abnormalities preceding, or occurring during, BC include overexpression of the BCR/ABL transcript, upregulation of the EVI1 gene, increased telomerase activity, and mutations of the tumor suppressor genes RB1, TP53, and CDKN2A. The cytogenetic evolution patterns vary significantly in relation to treatment given during CP. For example, +8 is more common after busulfan than hydroxyurea therapy, and the secondary changes seen after interferon-alpha treatment or bone marrow transplantation are often unusual, seemingly random, and occasionally transient. Apart from the strong phenotypic impact of addition of acute myeloid leukemia/myelodysplasia-associated translocations and inversions, such as inv(3)(q21q26), t(3;21)(q26;q22), and t(15;17)(q22;q12-21), in CML BC, only a few significant differences between myeloid and lymphoid BC are discerned, with i(17q) and TP53 mutations being more common in myeloid BC and monosomy 7, hypodiploidy, and CDKN2A deletions being more frequent in lymphoid BC. The prognostic significance of the secondary genetic changes is not uniform, although abnormalities involving chromosome 17, e.g., i(17q), have repeatedly been shown to be ominous. However, the clinical impact of additional cytogenetic and molecular genetic aberrations is most likely modified by the treatment modalities used.

Cytogenetics of chronic myelogenous leukaemia

The Philadelphia (Ph) chromosome is present in the leukaemic cells of most patients with chronic myelogenous leukaemia. Variant translocations occur in 10% of patients but breakpoints on chromosomes 9 and 22 remain the same, so prognosis of these patients is unchanged. Clonal evolution is infrequent in chronic phase and its significance depends on the specific chromosome involved, the number of metaphases affected and the timing in the chronic phase. The majority of patients in blastic phase demonstrate clonal evolution; three specific abnormalities (+Ph, +8 and isochromosome 17q) are present in 70% of patients. Loss of the Ph chromosome on therapy is associated with prolonged survival. For monitoring these events conventional G-band cytogenetics (CG) is essential at presentation to characterize the Disease cytogenetically, while fluorescence in situ hybridization (FISH) on hypermetaphase preparations (hypermetaphase FISH (HMF)) is important for establishing the specific frequency of Ph+ cells. During treatment FISH on interphase cells (I-FISH) can monitor the level of Ph+ cells in circulation, while CG may be used to identify any suspected clonal evolution. Where I-FISH is negative, HMF is essential to evaluate minimal residual disease.

Identification of variant translocations in chronic myeloid leukemia by fluorescence in situ hybridization

We studied two cases of chronic myeloid leukemia (CML) having variant complex translocations detected by trypsin G-banding and fluorescence in situ hybridization (FISH). Application of dual color- (DC-) FISH using abl and bor cosmid probes permitted us to detect the bor-abl fusion event on both interphase nuclei and metaphase spread. Furthermore, FISH using combinatorial hybridization (centromeric-library and library-library probes) demonstrated the content and the position of the translocations in CML patients with variant (complex type) Ph-positive rearrangements. FISH analysis appears to be superior than conventional cytogenetic analysis.

Identification of a conserved family of Meis1-related homeobox genes

Meis1 locus was isolated as a common site of viral integration involved in myeloid leukemia in BXH-2 mice. Meis1 encodes a novel homeobox protein belonging to the TALE (three amino acid loop extension) family of homeodomain-containing proteins. The homeodomain of Meis1 is the only known motif within the entire 390-amino-acid protein. Southern blot analyses using the Meis1 homeodomain as a probe revealed the existence family of Meis1-related genes (Mrgs) in several diverged species. In addition, the 3' untranslated region (UTR) Meis1 was remarkably conserved in evolution. To gain a further understanding of the role Meis1 plays in leukemia and development, as well as to identify conserved regions of the protein that might reveal function, we cloned and characterized Mrgs from the mouse and human genomes. We report the sequence of Mrg1 and MRG2 as well as their chromosomal locations in murine and human genomes. Both Mrgs share a high degree of sequence identity with the protein coding region of Meis1. We have also cloned the Xenopus laevis ortholog of (XMeis1). Sequence comparison of the murine and Xenopus clones reveals that Meis1 is highly conserved throughout its coding sequence as well as the 3' UTR. Finally, comparison of Meis1 and the closely related Mrgs to known homeoproteins suggests that Meis1 represents a new subfamily of TALE homeobox genes.

Molecular demonstration of BCR/ABL fusion in two cases with chronic myeloproliferative disorder carrying variant Philadelphia t(14;22)(q32;q11)

We report two cases with chronic myeloproliferative disorder which were found to carry simple variant Philadelphia (Ph) t(14;22)(q32;q11) in unstimulated bone marrow mononuclear cells. Both cases were characterized molecularly by Southern blot, reverse transcription-polymerase chain reaction (RT-PCR), and direct sequencing of the RT-PCR products. In the first case (female, aged 65, in blastic transformation which developed one year after the initial diagnosis of myelofibrosis), a t(14;22) (q32;q11) was found in association with several other chromosomal abnormalities [48,XX,+X,+5,del(5) (q12q32),+8,der(9)t(9;11)(q32;q11),-11]; molecular analysis demonstrated the presence of a BCR-ABL chimeric gene and mRNA transcript of the b2-a2 type. In the second case (female, aged 16, with clinical and hematologic features typical of chronic myelogenous leukemia in chronic phase), a t(14;22) (q32;q11) was identified as the sole karyotypic abnormality; again, molecular analysis demonstrated the presence of a BCR-ABL chimeric gene and mRNA transcript, this time of the b3-a2 type. Our findings further support the notion that, even when undetectable by conventional cytogenetics, band 9q34 participates in all Ph chromosomes and leads to the formation of chimeric BCR-ABL genes.

A novel translocation involving chromosomes 2, 9, 14, and 22 in chronic myeloid leukemia

A 46-year-old man with chronic myelogenous leukemia was found to have a new complex translocation. In chronic phase, all of the bone marrow cells had a rearrangement of a t(2;9;14;22) (p21;q34;q32;q11). Southern blot analysis of leukocyte DNA revealed rearrangement of the breakpoint cluster region (bcr) within the 5.8-Kb bcr. The patient eventually died in blast crisis 28 months later. The cytogenetic findings of bone marrow cells showed a 46,XY,t(2;9;14;22)(p21;q34;q32;q11),add(1p),del(3q) karyotype in blast crisis.

Complex translocations of the Ph chromosome and Ph negative CML arise from similar mechanisms, as evidenced by FISH analysis

The authors report on 13 patients with chronic myeloid leukemia (CML) studied by serial karyotyping and fluorescence in situ hybridization (FISH) of their bone marrow cells. Ten patients had complex translocations of the Ph chromosome while the remaining three were Ph negative. FISH analysis revealed in all 13 patients the translocation of the ABL protooncogene into chromosome 22 at band q11. Moreover, in all complex translocations but one, FISH with a chromosome 22 painting probe demonstrated on one chromosome 9 at band q34 the presence of material from chromosome 22, in addition to signals on the third chromosome involved in complex changes. Therefore, in this study complex translocations appeared as secondary changes resulting from two consecutive translocations with a total of at least four breaks. The first translocation gave rise to the standard t(9;22)(q34;q11). The second one included a break distal to the original breakpoint at band 9q34 and another one on a third chromosome. Furthermore FISH using S1 and S15 probes, mapped at band 22q11.2 or 22q12, gave evidence that in complex translocations the secondary breakpoint on der(9) was in the translocated segment 22q11-qter between bands q11 and q12. FISH analysis also disclosed the presence of material from chromosome 22 on one chromosome 9 in the three patients with Ph negative CML, demonstrating that in these cases a retranslocation between chromosomes 9q+ and 22q- had occurred. Consequently, the four-break mechanism could also be invoked for the three Ph negative CML patients.

Isodicentric Philadelphia chromosome in accelerated phase of chronic myeloid leukemia

We describe a case of chronic myeloid leukemia (CML) associated with the finding of an isodicentric Philadelphia chromosome [idic(Ph)] during the accelerated phase of the disease. Chromosome study was carried out on bone marrow aspirate cells, obtained and cultured 5 months after the clinical diagnosis. The presence of an isodicentric Philadelphia chromosome was found in 90% of the analyzed metaphases; among the remaining observed metaphases, 6% showed two idic(Ph) chromosomes, 2% a t(9;22), and 2% a normal karyotype. The patient died 7 months after the clinical diagnosis, and 2 months after our chromosome study. The observation of idic(Ph) during CML has seldom been reported and the few cases studied have been inconsistently correlated with the course of the disease. In the present case, the finding of an idic(Ph) and the short patient survival from the time of clinical diagnosis may suggest the observed chromosome aberration as a factor associated with a poor prognosis.

The cytogenetic scenario of chronic myeloid leukemia

The Philadelphia chromosome (Ph), i.e., the reciprocal translocation t(9;22)(q34;q11), is found with great specificity in bone marrow cells from patients with chronic myeloid leukemia (CML). Variant Ph-producing translocations, seen in 5-10% of all patients, are all complex and involve the same molecular rearrangement as the regular t(9;22). Patients with classic and variant Ph-producing translocations are clinically and hematologically identical, and as a group differ from Ph-negative CML patients. In all patient groups, the occurrence of additional chromosome changes is an ominous sign indicating that disease progression is imminent. The chromosome changes occurring in excess of the Ph in CML are clearly nonrandom and two pathways of cytogenetic evolution may be distinguished. Major route changes comprise trisomy 8, i(17q), trisomy 19, and an extra Ph; totally, 71% of Ph-positive CML patients have at least one of these four major route changes. Six minor route changes, including five numerical abnormalities (-7, -17, +17, +21, and -Y) but also one structural aberration, t(3;21) (q26;q22), have been identified. At least one of these changes is found in 15% of all Ph-positive CML cases. Altogether, the four major route aberrations and the six minor route changes are present as part of the clonal evolution in 86% of CML with cytogenetic abnormalities in addition to the Ph chromosome.

Complex translocation involving Ph chromosome in a patient with typical chronic myelogenous leukemia

We report a cytogenetic study of a patient with chronic myelogenous leukemia (CML) who, while displaying a Philadelphia (Ph) chromosome, resulting from a standard t(9;22) at diagnosis, during the chronic phase (CP) showed disappearance of the Ph and occurrence of new chromosome changes, including a marker probably arising from a translocation involving chromosome 17 and the Ph. In situ hybridization confirmed the cytogenetic appearance and demonstrated that the breakpoint on the Ph marker occurred below the BCR-ABL fusion gene.

Molecular cloning of the breakpoints of a complex Philadelphia chromosome translocation: identification of a repeated region on chromosome 17

Complex translocations in chronic myelogenous leukemia involve various chromosomes, in addition to chromosomes 9 and 22, in a nonrandom fashion. We have analyzed the DNA from leukemia cells characterized by a complex translocation, t(9;22;10;17)(q34;q11;p13;q21), by using the techniques of Southern blot hybridization, in situ hybridization, and molecular cloning; one of the breakpoints is at 17q21, a band that is frequently involved in complex 9;22 translocations. All of the breakpoint junctions and the corresponding normal sequences from the four involved chromosomes have been molecularly cloned. Restriction mapping is consistent with a simple concerted exchange of chromosomal material among the four chromosomes, except that additional changes appeared to have occurred within the chromosome 17 sequences. The cloned sequences on chromosome 17 at band q21 were found to be repeated in normal cells. By fluorescence in situ hybridization, a strong signal is seen at 17q21, but a weaker signal is also present at 17q23. By comparison with other primate species, an inversion in chromosome 17 during evolution appears to be responsible for the splitting of the cluster of repeat units in normal human cells.

Complex chromosomal translocations in the Philadelphia chromosome leukemias. Serial translocations or a concerted genomic rearrangement?

Joining of the BCR and ABL genes is an essential feature of the group of human leukemias characterized by the Philadelphia chromosome and there is recent evidence that the human BCR-ABL fusion gene induces leukemia in experimental animals. Joining of these two genes is the result of cytogenetic translocation, usually the t(9;22)(q34;q11), but sometimes of more complex translocations involving one or more chromosomes in addition to chromosomes 9 and 22. The leukemic cells of some patients carry the BCR-ABL fusion gene but have an apparently normal karyotype. Recent studies show that these cells conceal complex chromosome rearrangements. Because the BCR-ABL fusion gene appears to be the result of cytogenetic rearrangement in all cases of these leukemias, the causes and mechanism of chromosome rearrangement will be relevant to the development of leukemia in man. We examine mechanisms of chromosome rearrangement and propose that both simple and complex chromosome translocations result from a single, though sometimes complex, interchange event.

A complex chromosome rearrangement forms the BCR-ABL fusion gene in leukemic cells with a normal karyotype

Chromosome in situ hybridization studies showed that the normal karyotype of leukemic cells from a patient with Ph1-negative, BCR-positive chronic myeloid leukemia (CML) concealed a complex t(9;22;20)(q34;q11;p13). The close association of 5'-BCR and 3'-ABL was demonstrated by field inversion gel electrophoresis, and in situ hybridization showed that BCR-ABL was located on the short arm of chromosome 20. Our findings further indicate that chromosome rearrangement is the cause of BCR-ABL gene fusion in leukemic cells that show a normal karyotype. Results from in situ hybridization studies were consistent with formation of the t(9;22;20) by a two step chromosomal rearrangement, but field inversion gel electrophoresis results indicated a more complex rearrangement.

Chromosomal characteristics of chronic and blastic phase of chronic myeloid leukemia. A study of 100 patients in India

We report the cytogenetic findings of 100 patients with chronic myeloid leukemia (CML) [72 patients in chronic phase (CP) and 28 patients in blastic phase (BP)]. Of the 95 Ph + patients, six had Ph variant translocations involving chromosomes 1, 6, 7, 10, and 12. The percentage frequency of patients with chromosomal changes other than Ph was 7.3%. The additional aberrations (e.g., + Ph, + 8, i(17q), and + 19 were observed in 66.6% of BP patients. Of these anomalies, the frequency of + Ph and + 19 was higher in our patients than the incidence reported in literature. The association of + Ph and + 19 in patients with extramedullary T-cell blast crisis is an unusual finding as compared with reports in the literature and could be explained by geographic heterogeneity. The extra chromosomal abnormalities were almost absent in lymphoid blast crisis patients with blast phenotype of common acute lymphoblastic leukemia (ALL) type. Discrepancies were noted in different tissues (bone marrow and lymph node) in patients with extramedullary blast crisis of both myeloid and lymphoid type. These findings indicate the cytogenetic correlation with clinical and morphological picture, which consequently implicates the diagnostic and prognostic significance of chromosomal aspects.

The occurrence of variant Ph translocations in chronic myeloid leukemia (CML): a report of six cases

Variants of Philadelphia chromosome (Ph) translocation were detected in six of 95 Ph positive chronic myeloid leukemia (CML) patients (6.3 per cent). Two of these patients showed a Ph variant of 'simple' type, involving chromosomes 10 and 12. In four patients, the variant Ph was of 'complex' type involving a third chromosome:chromosomes 1, 6, 7 and 12 in addition to 9 and 22. Two of these resulted in the occurrence of a 'masked' Ph. In addition to variant Ph translocations, variant breakpoints such as q12 (two patients) and q13 (one patient) on chromosome 22 were observed in another three patients with t(9;22).

Complex translocations, simple variant translocations and Ph-negative cases in chronic myelogenous leukaemia

A proportion of cases of chronic myelogenous leukaemia (CML) has been described either (1) with a variant translocation, or (2) without the apparent involvement of both 9q34 and 22q11 (Ph-negative CML). All variant translocations have been further demonstrated to be complex implicating 9q34,22q11, plus another breakpoint on a variable chromosome. Complex translocations may be due to two successive events. Some of the breakpoints on the variable chromosome appear to be recurrent, and these remain to be studied for prognostic significance. Ph-negative CML comprises (1) cases of submicroscopic (hidden) insertion of 9q34-ABL within 22q11-BCR, and (2) cases without BCR-ABL rearrangement. We propose this last category to be called "CML-like disease", not to be confused anymore with true CML, and consequently to be studied as a separate entity.

Cytogenetic peculiarities in chronic myelogenous leukemia

Cytogenetic investigations were performed in 185 patients with chronic myelogenous leukemia (CML) at all stages of the disease; 166 patients were Ph positive-159 (95.8%) of these showing the standard Ph translocation, and 7 (4.2%) variant translocations-17 patients were Ph negative. In 2 patients the cytogenetic analysis was unsuccessful. Additional aberrations were found in 40 (24.1%) of the Ph-positive patients. Nine (52.9%) of the Ph-negative patients showed chromosome anomalies. Besides the well known nonrandom abnormalities (-7, +8, i(17q), +19, +Ph) we found a high frequency of clones with rare or not yet described structural rearrangements--in 14 cases (34.2%) of the Ph-positive patients and in 2 cases (20%) of the Ph-negative patients with other chromosome abnormalities. The clinical significance of these findings is discussed.

Radiation exposure and chromosome abnormalities. Human cytogenetic studies at the National Institute of Radiological Sciences, Japan, 1963-1988

The results of human cytogenetic studies performed at the National Institute of Radiological Sciences (NIRS), Chiba, Japan for about 25 years are described. The studies were pursued primarily under two major projects: one involving people exposed to radiation under various conditions and the other involving patients with malignant diseases, especially leukemias. Whereas chromosome abnormalities in radiation-exposed people are excellent indicators of radiation exposure, their behavior in bone marrow provide useful information for a better understanding of chromosome abnormalities in leukemias and related disorders. The role of chromosome abnormalities in the genesis and development of leukemia and related disorders is considered, suggesting a view for future studies in this field.

Distribution of breakpoint within the breakpoint cluster region (bcr) in chronic myelogenous leukemia with a complex Philadelphia chromosome translocation

We analyzed, by Southern blot hybridization, the site of breakpoint within the breakpoint cluster region (bcr) in six patients with a complex Philadelphia chromosome (Ph) translocation and in 23 unselected patients with a standard Ph. The breakpoint was found within the 5.8 kb bcr in all 29 patients. When the bcr was subdivided into four parts, fragments I-IV, based on the restriction enzyme sites, among the six patients with a complex Ph, two had a breakpoint at fragment I, three at fragment II, and one at fragment III. This distribution of breakpoints in patients with a complex Ph did not differ significantly from that in patients with a standard Ph. A deletion of an allele within the bcr was found in three patients (50%) with a complex Ph and in three (13%) with a standard Ph. The internal bcr deletion may be more common in patients with a complex Ph.

Cytogenetic and molecular studies in patients with chronic myeloid leukemia and variant Philadelphia translocations

Out of 105 Philadelphia (Ph) positive chronic myeloid leukemia patients analyzed, six (5.7%) carried a variant Ph translocation, namely t(6;9;9;10;22)(q24;p13;q34;p15;q11); t(9;13;22)(q34;q21;q11);der(2)(2pter----2q31::9q21---- 9q34::22q11----22qter) and der(9)t(2;9) (9pter----9q21::2q31----2qter);t(7;9;22)(q11;q34 ;q11), 14q + ;t(7;9;22)(q35;q34;q11), and t(9;11;22) (q34;q13;q11), respectively. Five of these patients were analyzed with Southern blotting. Three of them showed an atypical molecular pattern; namely, the patient with t(9;13;22) showed no rearrangement in the breakpoint cluster region (bcr), the patient with t(7;9;22)(q35;q34;q11) showed a 3' deletion, and the patient with t(7;9;22), 14q + showed a bcr rearrangement 3' to the exon 4 of the M-BCR. Chromosome in situ hybridization studies demonstrated that in patient one, a two-step translocation occurred: the first step moved the 3' bcr from chromosome 22 to chromosome 9, and the second moved the terminal part of 22q, carrying the c-sis protooncogene, to 10p. Variant Ph translocations appear to be associated with atypical molecular breakpoints.

Rejoining between 9q+ and Philadelphia chromosomes results in normal-looking chromosomes 9 and 22 in Ph1-negative chronic myelocytic leukemia

Rearrangement of the breakpoint cluster region (bcr) and the chromosomal location of c-abl and 3'-bcr were studied in two patients with Philadelphia chromosome (Ph1)-negative chronic myelocytic leukemia (CML). One patient (patient 1) had a normal karyotype and the other (patient 2), 46,XY,inv(3)(q21q26). Both patients showed the bcr rearrangement by Southern blot analysis with a 1.2kb 3'-bcr probe. In situ hybridization studies demonstrated the location of the homologous sequences of bcr on chromosome 22 in patient 1, and on chromosomes 9 and 22 in patient 2. These findings indicate that the morphologically normal-looking chromosomes 9 and 22 in patient 2 are the result of a retranslocation between chromosomes 9q+ and 22q-, abnormalities which were first formed by a standard Ph1 translocation.

Chromosomal in situ hybridization and Southern blot analyses using c-abl, c-sis, or bcr probe in chronic myelogenous leukemia cells with variant Philadelphia translocations

The Philadelphia (Ph) chromosome is a cytogenetic hallmark of chronic myelogenous leukemia (CML). Whereas the majority of Ph-positive CML patients show the standard Ph translocation involving chromosomes 9 and 22, t(9;22)(q34;q11), the minority of cases exhibit a variant type of Ph translocation involving these two and other chromosomes (complex type) or those involving #22 and chromosomes other than #9 (simple type). To get an insight into the nature of variant Ph translocations and the process of their formation, we examined the localization of the c-abl and c-sis oncogenes and the breakpoint cluster region (bcr) gene by chromosomal in situ hybridization in ten variant Ph translocations of CML including five simple and five complex ones as initially interpreted. In situ hybridization showed that c-abl localized to band 9q34 and c-sis localized to band 22q12-q13 were translocated on the Ph and on one of the rearranged chromosomes other than #9, respectively, in all the variant translocations examined. On the other hand, bcr localized to band 22q11 was translocated on various chromosomes but mostly on chromosome 9. Parallel Southern blot analyses on DNA from leukemic cells of five patients including two with simple translocations and three with complex ones revealed rearrangements of bcr with breakpoints occurring mostly in a 5' portion of 5.8-kb BamHI/BglII sequences, which are quite similar to those detected so far in CML cases with the standard Ph translocation. The present findings strongly suggest that variant Ph translocations of CML are all complex, and some of them are formed stepwisely from the standard translocation.

Translocation (8;21) and its variants in acute nonlymphocytic leukemia. The relative importance of chromosomes 8 and 21 to the genesis of the disease

Chromosome analysis was performed in 25 patients with acute nonlymphocytic leukemia (ANLL), mostly of the M2 type. Eighteen had the standard translocation, t(8;21)(q22;q22), four had complex translocations involving 1p36, 11p13, 17p11, and 17p23, respectively, with chromosomes 8 and 21, and the remaining three patients had simple translocations, one with t(3;21)(p14;q22) and two with t(16;21)(p11;q22), without involving chromosome 8. Chromosome abnormalities additional to t(8;21) and its variants that were most frequently observed were -X, -Y, and del(9). Complex translocations are thought to be derived from the standard translocation and to be essentially similar in nature. The finding that chromosome 21 was involved in all of the standard, simple, and complex translocations, and that chromosome 8 was not involved in simple variants suggest a greater weight of chromosome 21 in the relative importance of the two chromosomes to the genesis of ANLL.