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Fluorescence In Situ Hybridization Analysis of Complex Translocations in Two Newly Diagnosed Philadelphia Chromosome-Positive Chronic Myelogenous Leukemia Patients
Fluorescence In Situ Hybridization Analysis of Complex Translocations in Two Newly Diagnosed Philadelphia Chromosome-Positive Chronic Myelogenous Leukemia Patients E. Rajcan-Separovic, I. Bence-Bruckler, P. Wells, and H. Wang
ABSTRACT: Two different complex translocations from newly diagnosed cases of Philadelphia chromosome-positive chronic myelogenous leukemia (CML) were characterized by G-banding and fluorescence in situ hybridization (FISH) analysis. In one case, a unique balanced t(9;22;9;11) (q34;q11;p22;q23) was identified by G-banding, and confirmed by FISH using MBCR/ABL and painting probes. In the second case, an apparently balanced t(19;22) was identified by G-banding analysis. FISH using MBCR/ABL probe detected the fusion gene on the derivative chromosome 22, indicating the involvement of chromosome 9. Further FISH analysis with selected painting probes showed that the t(19;22) was a result of a complex translocation involving chromosomes 9, 19, 21, and 22. © Elsevier Science Inc., 1999. All rights reserved. INTRODUCTION
CASE REPORTS
The Philadelphia (Ph) chromosome is the most consistent chromosomal abnormality in patients with chronic myelogenous leukemia (CML) [1]. In the majority of cases, the Ph chromosome arises from a reciprocal translocation 9;22, with the C-ABL oncogene from 9q34 fused to the breakpoint cluster region (BCR) locus on chromosome 22 [2]. In 5–10% of patients with CML, the Ph chromosome originates from other rearrangements than the classical t(9;22). A simple variant Ph-producing translocation involves chromosome 22 and a chromosome other than 9, while a complex variant translocation involves three or more chromosomes [3, 4]. In almost all cases with variant Ph chromosome, the BCR/ABL rearrangement can be detected at the molecular level or by in situ hybridization [5, 6]. In this report, we describe complex translocations with variant Ph chromosomes in two patients with newly diagnosed CML.
Case 1 The patient was a 75-year-old male who underwent routine physical investigation. His medical history indicated mild diabetes and mild Alzheimer’s disease. His blood work showed a hemoglobin of 123 g/L, platelet count of 422 3 109/L, and a white cell count of 17.8 3 109/L, with a left shift in the granulocytic series with an eosinophil count of 0.5 3 109/L and a basophil count of 0.2 3 109/L. At the time of referral, the patient had no health complaints. The bone marrow aspirate and biopsy demonstrated a hypercellular marrow with increased megakaryocytes, all stages of maturation of granulopoieses with 10– 15% blasts and promyelocytes. There was mild basophilia in the marrow. Erythropoiesis was normoblastic with all stages of development present; however, the myeloid:erythroid ratio was altered, and was 20:1, due to the granulocytic hyperplasia. A diagnosis of CML was made and the patient remained in stable remission on hydroxyurea 500 mg, alternating with 1000 mg, on a daily basis for the last 18 months.
From the Cytogenetics Laboratory, Department of Pathology, B. C. Children’s Hospital (E. R.-S.), Vancouver, British Columbia, Canada; the Hematology Department, Ottawa Hospital (I. B.-B., P. W.), Ottawa, Ontario, Canada; and the Cytogenetics Laboratory, Children’s Hospital of Eastern Ontario (H. W.), Ottawa, Ontario, Canada. Address reprint requests to: Dr. Evica Rajcan-Separovic, Department of Pathology, Cytogenetics, 4480 Oak Street, B. C. Children’s Hospital, Vancouver, British Columbia, V6H 3V4, Canada. Received January 20, 1999; accepted March 1, 1999. Cancer Genet Cytogenet 114:71–74 (1999) Elsevier Science Inc., 1999. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
Case 2 A 41-year-old patient presented with a complaint of upper quadrant pain and bifrontal headache. There was no history of fever, night sweats, or weight loss. He also had no history of bleeding or bruising. His past medical history was unremarkable. On examination, massive splenomegaly and hepatomegaly was detected. A complete blood
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Figure 1 G-banded karyotype of a cell showing t(9;22;9;11)(q34;q11;p22;q23) in case 1. The chromosomes involved in the translocation are marked by arrows.
work revealed a complete blood count of 324 3 109/L, with a left shift of granulocyte series as well as basophilia and eosinophilia. The platelet count was 287 3 109/L and hemoglobin was 79 g/L. A diagnosis of CML was made and the patient was admitted to the hospital for
management of hyperleukocytosis. Therapy with hydroxyurea was initiated, and 2 months after the diagnosis, the patient underwent an allogeneic peripheral blood stem cell transplantation for his chronic-phase CML.
Figure 2 G-banded karyotype of a cell showing t(19;22)(q13;q11) in case 2. The chromosomes involved in translocation as determined by FISH are marked with arrows.
73
FISH Analysis of Complex Translocations in CML METHODS Cytogenetic analyses were performed on G-banded metaphases obtained from 24- and 48-hour unstimulated bone marrow cultures in case 1, and from unstimulated 24-hour peripheral blood cultures in case 2 as previously described [7]. Twenty cells from each case were analyzed. Fluorescence in situ hybridization procedures were performed as suggested by the manufacturer (ONCOR, Gaithesburg, MD, USA). Briefly, metaphase preparations were denatured for 2 minutes in 70% formamide/2 3 SSC (pH 7.0 at 708C). Following dehydration, the metaphase preparations were hybridized with appropriate probes overnight in a humid chamber at 378C. The final stringency of the post-hybridization washes was 2 3 SSC at 458C. Biotin- or digoxigenin-labeled whole chromosome painting probes for chromosomes 9, 11, 19, 21, and 22 were used. For the detection of the BCR/ABL fusion gene, a two-color M-BCR/ABL probe with DAPI-4, 6-diamino-2 phenyl-indole as counterstain was used. The images were collected on an Olympus microscope equipped with a CCD camera operated by an Applied Imaging system.
RESULTS The G-banded karyotype of case 1 at diagnosis was determined as 46,XY,t(9;22;9;11)(q34;q11;p22;q23) (Fig. 1). The M-BCR/ABL dual-color probe produced an ABL signal on the normal chromosome 9 at q34, a BCR signal on the normal chromosome 22 at q11, and a fused signal on the Ph chromosome. The chromosome 9 painting probe hybridized to the normal 9, the der(9), the distal q end of der(11), and the Ph chromosome. The chromosome 11 painting probe hybridized to the normal 11, the der(11), and the distal q region of the der(9). This analysis confirmed the G-banding result. In case 2, the Ph chromosome was initially identified as derived from a simple variant translocation 19;22 by Gbanding analysis (Fig. 2). Fluorescence in situ hybridization using an M-BCR/ABL probe produced a fused gene signal on the Ph chromosome, indicating the involvement of chromosome 9. Further FISH analysis using selected chromosome painting probes was carried out. The chromosome 9 painting probe hybridized to both chromosome 9 homologs evenly and the terminal end of the Ph chromosome, while the chromosome 19 probe hybridized to the normal 19, the der(19), and the terminal end of one Ggroup chromosome (Fig. 3A). The chromosome 22 painting probe hybridized evenly to the normal chromosome 22, the Ph chromosome, and chromosome 19. When the chromosome 21 painting probe was used, the distal segment of one chromosome 21 was not painted, suggesting the presence of chromosome 19 material. On re-evaluation of G-banded chromosomes, the terminal ends of 21q and 9q appeared different between the homologs, indicating that the distal end of one chromosome 21 might be replaced by 19q and translocated to 9q. However, chromosome 21 paint was not detected on any chromosome other than 21, suggesting that, if there was a break at the terminal end of one chromosome 21, the segment produced was
Figure 3 FISH analysis of case 2 showing (A) hybridization of chromosome 19 painting probe to normal and derivative chromosome 19 (arrows) and a G-group chromosome (arrowhead); and (B) hybridization of chromosome 21 painting probe to chromosom 21 homologs (arrows).
too small to be detected on 9q, or alternatively, it was deleted. The variant translocation can therefore conditionally be designated as t(9;22;19;21)(q34;q11;q13;q22). DISCUSSION The complex translocation in case 1 involved chromosome bands 9p22 and 11q23 in addition to the standard 9q34 and 22q11. Chromosome 11 is known to be frequently involved in complex translocations that produce a Ph chromosome in CML, although the breakpoints appear to cluster at 11q13 [8, 9]. The involvement of bands 9p22, 11q23, 22q11, and 9q34 had been reported previously in two cases of blastic-phase CML [10, 11]. These translocations were, however, described as t(11;9)(9;22) (q23;p22q34;q11) and the t(9;11), also known to be associated with AML-M5 [9], was believed to be a secondary ab-
74 erration in a clone containing the standard t(9;22). Translocation (19;22) as seen in our case 2 has also been previously described in patients with CML [12], and the complex nature of this translocation involving chromosomes 1, 9, 19, and 22 elucidated by FISH [13]. In our case, however, FISH analysis has revealed that a different set of changes involving chromosomes 9, 19, 21, and 22 has contributed to the complex nature of the apparently balanced t(19;22). In both case 1 and 2, the presence of complex translocations was detected in all cells examined at diagnosis; however, the possibility of the existence of additional clone(s) in very low frequencies cannot be excluded. The mechanisms of these rearrangements are therefore difficult to determine, and the serial translocation or a single event can be considered [14]. The association of clonal changes in addition to a t(9;22) with disease progression is well known, but the clinical significance of complex variant translocations found at initial diagnosis is not clear. It has been observed that patients carrying simple or complex Ph translocations do not differ in hematologic and clinical features [15]. With continued clinical and cytogenetic follow-up of our patients, we hope to be able to determine if there is any prognostic significance associated with these translocations. REFERENCES 1. Rowley JD (1973): A new consistent chromosomal abnormality in chronic myelogenous leukemia identified by quinacrine fluorescence and Giemsa staining. Nature 243:290–293. 2. de Klein A, Geurts van Kessel A, Grosveld G, Bartram CR, Hagemeijer A, Bootsma D, Spurr NK, Heisterkamp N, Groffen J, Stephenson JR (1982): A cellular oncogene is translocated to the Philadelphia chromosome in chronic myelocytic leukemia. Nature 300:765–767. 3. Mitelman F (1993): The cytogenetic scenario of chronic myeloid leukemia. Leuk Lymphoma (Suppl.) 1:11–15.
E. Rajcan-Separovic et al. 4. Huret JL (1990): Complex translocations, simple variant translocations and Ph-negative cases in chronic myelogenous leukemia. Hum Genet 85:565–568. 5. Sessarego M, Martinelli G, Chiamenti A, Defferrari R, Fugazza G, Bruzzone R, Ajmar F, Pignatti F (1993): Molecular analysis of six variant Philadelphia chromosome translocations in chronic myeloid leukemia. Cancer Genet Cytogenet 76:50–54. 6. Tosi S, Cabot G, Giudici G, Attuati V, Morandi P, Rambaldi A, Dohner H, Biondi A (1996): Detection of the breakpoint cluster region-ABL fusion in chronic myeloid leukemia with variant Philadelphia chromosome translocations by in situ hybridization. Cancer Genet Cytogenet 89:153–156. 7. Verma RS, Babu A (1995): Human Chromosomes: Principles and Techniques. McGraw-Hill, New York. 8. Abe S, Shiga Y, Ookoshi T, Tanaka T, Maruyama Y (1991): A complicated translocation involving five chromosomes (nos. 9, 11, 12, 21, 22) in patient with chronic myelocytic leukemia (CML). Int J Hematol 54:479–482. 9. Heim S, Mitelman F (1995): Cancer Cytogenetics, 2nd Ed. John Wiley & Sons Inc., New York. 10. Li L, Ritterbach J, Harbott W, Schroyens W, Lohmeyer H, Pralle H, Lampbert F (1993): Blastic phase chronic myeloid leukemia with a four break rearrangement: t(11;9)(9;22) (q23;p22q34;q11). Cancer Genet Cytogenet 68:131–134. 11. Dastugue N, Duchayne E, Huguet F, Demur C, Plaisancie H, Calvas P, Bourrouillou G, Pris J, Colombies P (1992): t(9;11) (p22;q23) translocation in blastic phase of chronic myeloid leukemia. Cancer Genet Cytogenet 63:37–42. 12. Mitelman F (1994): Catalog of Chromosome Aberrations in Cancer, 5th Ed. Wiley-Liss, New York. 13. Morris C, Fitzgerald P (1987): Complexity of an apparently simple variant Ph translocation in chronic myeloid leukemia. Leuk Res 11:163–169. 14. Fitzgerald P, Morris C (1991): Complex chromosomal translocations in the Philadelphia chromosome leukemias-serial translocations or a concerted genomic rearrangement. Cancer Genet Cytogenet 57:143–151. 15. Kantarijian HM, Deisseroth A, Kurtzrock R, Estrov Z, Talpaz M (1993): Chronic myelogenous leukemia. A concise update. Blood 82:691–703.
ABSTRACT: Two different complex translocations from newly diagnosed cases of Philadelphia chromosome-positive chronic myelogenous leukemia (CML) were characterized by G-banding and fluorescence in situ hybridization (FISH) analysis. In one case, a unique balanced t(9;22;9;11) (q34;q11;p22;q23) was identified by G-banding, and confirmed by FISH using MBCR/ABL and painting probes. In the second case, an apparently balanced t(19;22) was identified by G-banding analysis. FISH using MBCR/ABL probe detected the fusion gene on the derivative chromosome 22, indicating the involvement of chromosome 9. Further FISH analysis with selected painting probes showed that the t(19;22) was a result of a complex translocation involving chromosomes 9, 19, 21, and 22. © Elsevier Science Inc., 1999. All rights reserved. INTRODUCTION
CASE REPORTS
The Philadelphia (Ph) chromosome is the most consistent chromosomal abnormality in patients with chronic myelogenous leukemia (CML) [1]. In the majority of cases, the Ph chromosome arises from a reciprocal translocation 9;22, with the C-ABL oncogene from 9q34 fused to the breakpoint cluster region (BCR) locus on chromosome 22 [2]. In 5–10% of patients with CML, the Ph chromosome originates from other rearrangements than the classical t(9;22). A simple variant Ph-producing translocation involves chromosome 22 and a chromosome other than 9, while a complex variant translocation involves three or more chromosomes [3, 4]. In almost all cases with variant Ph chromosome, the BCR/ABL rearrangement can be detected at the molecular level or by in situ hybridization [5, 6]. In this report, we describe complex translocations with variant Ph chromosomes in two patients with newly diagnosed CML.
Case 1 The patient was a 75-year-old male who underwent routine physical investigation. His medical history indicated mild diabetes and mild Alzheimer’s disease. His blood work showed a hemoglobin of 123 g/L, platelet count of 422 3 109/L, and a white cell count of 17.8 3 109/L, with a left shift in the granulocytic series with an eosinophil count of 0.5 3 109/L and a basophil count of 0.2 3 109/L. At the time of referral, the patient had no health complaints. The bone marrow aspirate and biopsy demonstrated a hypercellular marrow with increased megakaryocytes, all stages of maturation of granulopoieses with 10– 15% blasts and promyelocytes. There was mild basophilia in the marrow. Erythropoiesis was normoblastic with all stages of development present; however, the myeloid:erythroid ratio was altered, and was 20:1, due to the granulocytic hyperplasia. A diagnosis of CML was made and the patient remained in stable remission on hydroxyurea 500 mg, alternating with 1000 mg, on a daily basis for the last 18 months.
From the Cytogenetics Laboratory, Department of Pathology, B. C. Children’s Hospital (E. R.-S.), Vancouver, British Columbia, Canada; the Hematology Department, Ottawa Hospital (I. B.-B., P. W.), Ottawa, Ontario, Canada; and the Cytogenetics Laboratory, Children’s Hospital of Eastern Ontario (H. W.), Ottawa, Ontario, Canada. Address reprint requests to: Dr. Evica Rajcan-Separovic, Department of Pathology, Cytogenetics, 4480 Oak Street, B. C. Children’s Hospital, Vancouver, British Columbia, V6H 3V4, Canada. Received January 20, 1999; accepted March 1, 1999. Cancer Genet Cytogenet 114:71–74 (1999) Elsevier Science Inc., 1999. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
Case 2 A 41-year-old patient presented with a complaint of upper quadrant pain and bifrontal headache. There was no history of fever, night sweats, or weight loss. He also had no history of bleeding or bruising. His past medical history was unremarkable. On examination, massive splenomegaly and hepatomegaly was detected. A complete blood
0165-4608/99/$–see front matter PII S0165-4608(99)00047-3
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E. Rajcan-Separovic et al.
Figure 1 G-banded karyotype of a cell showing t(9;22;9;11)(q34;q11;p22;q23) in case 1. The chromosomes involved in the translocation are marked by arrows.
work revealed a complete blood count of 324 3 109/L, with a left shift of granulocyte series as well as basophilia and eosinophilia. The platelet count was 287 3 109/L and hemoglobin was 79 g/L. A diagnosis of CML was made and the patient was admitted to the hospital for
management of hyperleukocytosis. Therapy with hydroxyurea was initiated, and 2 months after the diagnosis, the patient underwent an allogeneic peripheral blood stem cell transplantation for his chronic-phase CML.
Figure 2 G-banded karyotype of a cell showing t(19;22)(q13;q11) in case 2. The chromosomes involved in translocation as determined by FISH are marked with arrows.
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FISH Analysis of Complex Translocations in CML METHODS Cytogenetic analyses were performed on G-banded metaphases obtained from 24- and 48-hour unstimulated bone marrow cultures in case 1, and from unstimulated 24-hour peripheral blood cultures in case 2 as previously described [7]. Twenty cells from each case were analyzed. Fluorescence in situ hybridization procedures were performed as suggested by the manufacturer (ONCOR, Gaithesburg, MD, USA). Briefly, metaphase preparations were denatured for 2 minutes in 70% formamide/2 3 SSC (pH 7.0 at 708C). Following dehydration, the metaphase preparations were hybridized with appropriate probes overnight in a humid chamber at 378C. The final stringency of the post-hybridization washes was 2 3 SSC at 458C. Biotin- or digoxigenin-labeled whole chromosome painting probes for chromosomes 9, 11, 19, 21, and 22 were used. For the detection of the BCR/ABL fusion gene, a two-color M-BCR/ABL probe with DAPI-4, 6-diamino-2 phenyl-indole as counterstain was used. The images were collected on an Olympus microscope equipped with a CCD camera operated by an Applied Imaging system.
RESULTS The G-banded karyotype of case 1 at diagnosis was determined as 46,XY,t(9;22;9;11)(q34;q11;p22;q23) (Fig. 1). The M-BCR/ABL dual-color probe produced an ABL signal on the normal chromosome 9 at q34, a BCR signal on the normal chromosome 22 at q11, and a fused signal on the Ph chromosome. The chromosome 9 painting probe hybridized to the normal 9, the der(9), the distal q end of der(11), and the Ph chromosome. The chromosome 11 painting probe hybridized to the normal 11, the der(11), and the distal q region of the der(9). This analysis confirmed the G-banding result. In case 2, the Ph chromosome was initially identified as derived from a simple variant translocation 19;22 by Gbanding analysis (Fig. 2). Fluorescence in situ hybridization using an M-BCR/ABL probe produced a fused gene signal on the Ph chromosome, indicating the involvement of chromosome 9. Further FISH analysis using selected chromosome painting probes was carried out. The chromosome 9 painting probe hybridized to both chromosome 9 homologs evenly and the terminal end of the Ph chromosome, while the chromosome 19 probe hybridized to the normal 19, the der(19), and the terminal end of one Ggroup chromosome (Fig. 3A). The chromosome 22 painting probe hybridized evenly to the normal chromosome 22, the Ph chromosome, and chromosome 19. When the chromosome 21 painting probe was used, the distal segment of one chromosome 21 was not painted, suggesting the presence of chromosome 19 material. On re-evaluation of G-banded chromosomes, the terminal ends of 21q and 9q appeared different between the homologs, indicating that the distal end of one chromosome 21 might be replaced by 19q and translocated to 9q. However, chromosome 21 paint was not detected on any chromosome other than 21, suggesting that, if there was a break at the terminal end of one chromosome 21, the segment produced was
Figure 3 FISH analysis of case 2 showing (A) hybridization of chromosome 19 painting probe to normal and derivative chromosome 19 (arrows) and a G-group chromosome (arrowhead); and (B) hybridization of chromosome 21 painting probe to chromosom 21 homologs (arrows).
too small to be detected on 9q, or alternatively, it was deleted. The variant translocation can therefore conditionally be designated as t(9;22;19;21)(q34;q11;q13;q22). DISCUSSION The complex translocation in case 1 involved chromosome bands 9p22 and 11q23 in addition to the standard 9q34 and 22q11. Chromosome 11 is known to be frequently involved in complex translocations that produce a Ph chromosome in CML, although the breakpoints appear to cluster at 11q13 [8, 9]. The involvement of bands 9p22, 11q23, 22q11, and 9q34 had been reported previously in two cases of blastic-phase CML [10, 11]. These translocations were, however, described as t(11;9)(9;22) (q23;p22q34;q11) and the t(9;11), also known to be associated with AML-M5 [9], was believed to be a secondary ab-
74 erration in a clone containing the standard t(9;22). Translocation (19;22) as seen in our case 2 has also been previously described in patients with CML [12], and the complex nature of this translocation involving chromosomes 1, 9, 19, and 22 elucidated by FISH [13]. In our case, however, FISH analysis has revealed that a different set of changes involving chromosomes 9, 19, 21, and 22 has contributed to the complex nature of the apparently balanced t(19;22). In both case 1 and 2, the presence of complex translocations was detected in all cells examined at diagnosis; however, the possibility of the existence of additional clone(s) in very low frequencies cannot be excluded. The mechanisms of these rearrangements are therefore difficult to determine, and the serial translocation or a single event can be considered [14]. The association of clonal changes in addition to a t(9;22) with disease progression is well known, but the clinical significance of complex variant translocations found at initial diagnosis is not clear. It has been observed that patients carrying simple or complex Ph translocations do not differ in hematologic and clinical features [15]. With continued clinical and cytogenetic follow-up of our patients, we hope to be able to determine if there is any prognostic significance associated with these translocations. REFERENCES 1. Rowley JD (1973): A new consistent chromosomal abnormality in chronic myelogenous leukemia identified by quinacrine fluorescence and Giemsa staining. Nature 243:290–293. 2. de Klein A, Geurts van Kessel A, Grosveld G, Bartram CR, Hagemeijer A, Bootsma D, Spurr NK, Heisterkamp N, Groffen J, Stephenson JR (1982): A cellular oncogene is translocated to the Philadelphia chromosome in chronic myelocytic leukemia. Nature 300:765–767. 3. Mitelman F (1993): The cytogenetic scenario of chronic myeloid leukemia. Leuk Lymphoma (Suppl.) 1:11–15.
E. Rajcan-Separovic et al. 4. Huret JL (1990): Complex translocations, simple variant translocations and Ph-negative cases in chronic myelogenous leukemia. Hum Genet 85:565–568. 5. Sessarego M, Martinelli G, Chiamenti A, Defferrari R, Fugazza G, Bruzzone R, Ajmar F, Pignatti F (1993): Molecular analysis of six variant Philadelphia chromosome translocations in chronic myeloid leukemia. Cancer Genet Cytogenet 76:50–54. 6. Tosi S, Cabot G, Giudici G, Attuati V, Morandi P, Rambaldi A, Dohner H, Biondi A (1996): Detection of the breakpoint cluster region-ABL fusion in chronic myeloid leukemia with variant Philadelphia chromosome translocations by in situ hybridization. Cancer Genet Cytogenet 89:153–156. 7. Verma RS, Babu A (1995): Human Chromosomes: Principles and Techniques. McGraw-Hill, New York. 8. Abe S, Shiga Y, Ookoshi T, Tanaka T, Maruyama Y (1991): A complicated translocation involving five chromosomes (nos. 9, 11, 12, 21, 22) in patient with chronic myelocytic leukemia (CML). Int J Hematol 54:479–482. 9. Heim S, Mitelman F (1995): Cancer Cytogenetics, 2nd Ed. John Wiley & Sons Inc., New York. 10. Li L, Ritterbach J, Harbott W, Schroyens W, Lohmeyer H, Pralle H, Lampbert F (1993): Blastic phase chronic myeloid leukemia with a four break rearrangement: t(11;9)(9;22) (q23;p22q34;q11). Cancer Genet Cytogenet 68:131–134. 11. Dastugue N, Duchayne E, Huguet F, Demur C, Plaisancie H, Calvas P, Bourrouillou G, Pris J, Colombies P (1992): t(9;11) (p22;q23) translocation in blastic phase of chronic myeloid leukemia. Cancer Genet Cytogenet 63:37–42. 12. Mitelman F (1994): Catalog of Chromosome Aberrations in Cancer, 5th Ed. Wiley-Liss, New York. 13. Morris C, Fitzgerald P (1987): Complexity of an apparently simple variant Ph translocation in chronic myeloid leukemia. Leuk Res 11:163–169. 14. Fitzgerald P, Morris C (1991): Complex chromosomal translocations in the Philadelphia chromosome leukemias-serial translocations or a concerted genomic rearrangement. Cancer Genet Cytogenet 57:143–151. 15. Kantarijian HM, Deisseroth A, Kurtzrock R, Estrov Z, Talpaz M (1993): Chronic myelogenous leukemia. A concise update. Blood 82:691–703.