The Philadelphia (Ph) chromosome in leukemia. II. Variant Ph translocations in acute lymphoblastic leukemia

Philadelphia chromosome positive acute lymphoblastic leukemia showing normal karyotype in G-banding chromosomal examination before chemotherapy

A 29-year-old male was admitted because of thrombocytopenia. A diagnosis of acute lymphoblastic leukaemia was made on the basis of a 61.6% infiltration of leukemic cells in his bone marrow. Standard G-binding chromosome analysis of bone marrow cells revealed a normal karyotype. He received combination chemotherapy, and achieved hematological complete remission. However, chromosomal analysis of bone marrow cells after 2 courses of consolidation therapy showed the Philadelphia (Ph) chromosome in two cells out of 20 analysed. We retrospectively examined the sample of bone marrow cells before chemotherapy; It showed minor BCR/ABL positivity with FISH and RT-PCR methods. The Ph chromosome disappeared after consolidation chemotherapy and allogeneic bone marrow transplantation, but the Ph chromosome reappeared at relapse. We postulated that there were two clones, both a Ph-positive clone and Ph-negative clone. At the initial diagnosis, Ph chromosome was not detected because the G-banding method analyzed only metaphase cells, which contained few Ph-positive clones. In order to offer effective therapy with molecular targeting agents, in this poor prognostic disease, it is necessary to detect Ph chromosome before the first chemotherapy and BCR/ABL detection with FISH or RT-PCR methods appears more useful than G-banding chromosome analysis.

Double jeopardy from a single translocation: deletions of the derivative chromosome 9 in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is characterized by formation of a BCR-ABL fusion gene, usually as a consequence of the Philadelphia (Ph) translocation between chromosomes 9 and 22. Recently the development of new fluorescence in-situ hybridization (FISH) techniques has allowed identification of unexpected deletions of the reciprocal translocation product, the derivative chromosome 9, in 10% to 15% of patients with CML. These deletions are large, span the translocation breakpoint, and occur at the same time as the Ph translocation. Such deletions therefore give rise to previously unsuspected molecular heterogeneity from the very beginning of this disease, and there is mounting evidence for similar deletions associated with other translocations. Several studies have demonstrated that CML patients who carry derivative chromosome 9 deletions exhibit a more rapid progression to blast crisis and a shorter survival. Deletion status is independent of, and more powerful than, the Sokal and Hasford/European prognostic scoring systems. The poor prognosis associated with deletions is seen in patients treated with hydroxyurea or interferon, and preliminary evidence suggests that patients with deletions may also have a worse outcome than nondeleted patients following stem cell transplantation or treatment with imatinib. Poor outcome cannot be attributed to loss of the reciprocal ABL-BCR fusion gene expression alone, and is likely to reflect loss of one or more critical genes within the deleted region. The molecular heterogeneity associated with the Philadelphia translocation provides a new paradigm with potential relevance to all malignancies associated with reciprocal chromosomal translocations and/or fusion gene formation.

Adult precursor B-ALL with BCR/ABL gene rearrangements displays a unique immunophenotype based on the pattern of CD10, CD34, CD13 and CD38 expresssion

The Philadelphia chromosome (Ph+) reflects a balanced reciprocal translocation between the long arms of chromosomes 9 and 22 [t(9;22)(q34;q11.2] involving the BCR and ABL genes. At present, detection of BCR/ABL gene rearrangements is mandatory in precursor-B-ALL patients at diagnosis for prognostic stratification and treatment decision. In spite of the clinical impact, no screening method, displaying a high sensitive and specificity, is available for the identification of BCR/ABL+ precursor-B-ALL cases. The aim of the present study was to explore the immunophenotypic characteristics of precursor B-ALL cases displaying BCR/ABL gene rearrangements using multiple stainings analyzed by quantitative flow cytometry in order to rapidly (<1 h) identify unique phenotypes associated with this translocation. From the 82 precursor-B-ALL cases included in the study 12 displayed BCR/ABL gene rearragements, all corresponding to adult patients, four of which also displayed DNA aneuploidy. Our results show that BCR/ABL+ precursor B-ALL cases constantly displayed a homogeneous expression of CD10 and CD34 but low and relatively heterogeneous CD38 expression, together with an aberrant reactivity for CD13. In contrast, this unique phenotype was only detected in three out of 70 BCR/ABL cases. Therefore, the combined use of staining patterns for CD34, CD38 and CD13 expression within CD10-positive blast cells is highly suggestive of BCR/ABL gene rearrangements in adults with precursor B-ALL.

A new complex variant Philadelphia chromosome, t(1;9;22)ins(17;22), characterized by fluorescence in situ hybridization in an adult ALL

A new complex variant Philadelphia chromosome was detected in a 65-year-old man with acute, pre-B, lymphoblastic leukemia (ALL). The classic cytogenetic analysis identified an apparently balanced three-way translocation t(1;9;22)(q25;q34;q11.2). Fluorescence in situ hybridization (FISH) studies confirmed the translocation and showed bcr/abl fusion on the der(22). However, these studies revealed that the distal part of the bcr gene was not translocated onto chromosome 1 at 1q25, but inserted into chromosome 17 at 17p12-13. This complex variant translocation was described as a t(1;9;22)(q25;q34;q11.2)ins(17;22)(p12-13;q11.2q11.2). Secondary changes including +8, an inversion of the derivative chromosome 9, a translocation t(14;20)(q11;q13), and an additional derivative 22 were also identified in most of the abnormal cells. The patient died from systemic fungemia and multiorgan failure 9 months after the diagnosis of ALL. The clinical significance of complex variant Philadelphia chromosomes in ALL is reviewed and discussed.

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.

Characterization of a 14q+ marker chromosome in philadelphia chromosome positive acute lymphoblastic leukemia by DNA analysis and fluorescence in situ hybridization

We report a case of precursor-B acute lymphoblastic leukemia (ALL) with the Philadelphia chromosome (Ph) and a 14q+ chromosome whose additional material was a part of the long arm of der(9)t(9;22). A minor population carrying the standard Ph translocation without the 14q+ was also observed at the first presentation. The translocation of the BCR gene from chromosome 22 to the subtelomeric region of the 14q+ was confirmed by fluorescence in situ hybridization (FISH) using a yeast artificial chromosome (YAC) clone containing the BCR gene. The breakpoint of chromosome 14 could not be determined exactly but probably was at 14q24 or 14q32 by conventional chromosome analysis. Nevertheless, FISH using a YAC clone containing the human immunoglobulin heavy chain (IgH) gene locus, Southern blot, and pulsed-field gel electrophoresis (PFGE) analyses with IgJH probe, and loss of heterozygosity analysis at the alpha 1-antitrypsin (AT) gene locus showed lack of involvement of the IgH gene in the 14q+ and more centromeric breakage than the alpha 1-AT locus at 14q32.1. Thus, the formation of the 14q+ seemed to be a secondary genetic event after the Ph translocation and presumably played a minor role in the pathogenesis of B-cell malignancy in this case.

Cytogenetic and molecular analysis of a "masked" Philadelphia chromosome in chronic and blastic phases of chronic myeloid leukemia

A "masked" Philadelphia chromosome (Ph), t(1;22;9)(p32;q11;q34), was found in the bone marrow and peripheral blood cells of a patient with chronic myeloid leukemia (CML) during the chronic and blastic phases of the disease. As an additional change, a reciprocal translocation t(12;13)(p13;q14) was observed in the blastic phase. Southern blot analysis showed a rearrangement of the breakpoint cluster region (bcr). Northern blot analysis with a c-abl probe showed an abnormal 8.5 kb c-abl RNA transcript in addition to the normal 6- and 7-kilobase (kb) c-abl species. Thus, the results demonstrate the presence of a c-abl/bcr rearrangement in the masked Ph corresponding to that observed in the standard Ph translocation t(9;22)(q34;q11) of CML.

Masked Ph chromosome due to a new type of translocation in a patient with chronic myelogenous leukemia

A chronic myelogenous leukemia patient with a masked Ph chromosome due to a new type of translocation, t(9;11;22)(q34;p11;q11), is reported.

Cytogenetic and molecular characterization of a masked Philadelphia chromosome in chronic myelocytic leukemia

A case of typical chronic myeloid leukemia with an apparently Philadelphia-negative karyotype is described. Molecular studies confirmed the cytogenetic interpretation of a standard Ph rearrangement, with secondary involvement of 22q- in a translocation with chromosome #5, leading to its masking. The chromosomal regions engaged in the standard t(9;22) were not modified and the molecular rearrangements of Ph were also conserved. The hematologic and clinical features were apparently not influenced by the events leading to the masking of Ph. Further similar observations with both cytogenetic and molecular characterization are needed to better identify the possible clinical consequences of these complex changes.

The karyotype of blastic crisis

The nonrandomness of chromosome clonal evolution in blastic crisis of chronic myeloid leukemia is well established, with three major changes [+8, +Ph, i(17q)] occurring alone or in combination in over 70% of the patients. The chromosome changes observed in different tissues may reveal the origin of the abnormal clones, as well as provide evidence for distinct or common evolution by different cell populations. The significance of the chromosome abnormalities and their relationship to blastic conversion are discussed. In general, chromosome evolution may be considered a rather reliable predictive or diagnostic parameter of blastic crisis but both the nature and the subsequent behavior of abnormal clones appear to be of critical value. As to the clinical/chromosome correlations, a few major points have emerged: the i(17q) aberration is mostly associated with signs of myeloid differentiation of blasts and a marked basophilia; it is mainly observed in the late stage of the disease, but overall median survival of patients with this marker is usually long; more atypical or complex changes usually are associated with a worse prognosis; patients with only a Ph in their blasts may have a longer survival, at least in some cytologic subgroups; and d) the loss of the Y chromosome seems to protect the cell against further clonal evolution. Finally, the relevance of the chromosome changes in the multistage process of blastic conversion is discussed, and the breakpoints of secondary changes recorded so far are reviewed and examined. It appears that certain chromosome regions are more often affected; these might contain genes of critical importance for the final malignant progression. Molecular biology may provide insight, in the future, on the nature and expression of involved genes.

A case of chronic myeloid leukemia with a "masked" Philadelphia chromosome

A case is described of a 67-year-old man with chronic myeloid leukemia and a "masked" Philadelphia chromosome due to a translocation between chromosomes #4 and #22. The significance of this case in relation to the possible pathogenesis of chronic myeloid leukemia is discussed.

Four cases with complex Philadelphia translocations, including one with appearance de novo of a "masked" Ph

Four cases of chronic myelogenous leukemia (CML) with complex Philadelphia (Ph) translocations are described. The first case was that of a 50-year-old woman in the chronic phase of CML. Her leukemic cells showed a complex Ph translocation involving chromosomes #9, #11, and #22 [i.e., t(9;9;22;11)(11qter----11q11::9q11----9q34:: 9p11----9pter;22qter----22q11::9q34?;11 pter----11q11::22q11----22qter)]. In addition to the complex Ph translocation, the leukemic cells contained del(10)(p13). The second case was that of a 21-year-old man whose leukemic cells contained a translocation involving chromosomes #5, #9, and #22 [i.e., t(5;22;9)(q31;q11;q34)], resulting in a "masked" Ph chromosome. The third case was that of a 37-year-old man whose leukemic cells had a complex Ph translocation involving chromosomes #8, #9, and #22 [i.e., t(8;9;22)(q13;q34;q11)]. The fourth patient was a 41-year-old woman diagnosed as having CML in myeloid blastic phase, at which time the first specimen was examined by us. This blood sample showed a karyotype of 45,XX, -9, -17, -22, +mar1, +mar2,9q+. No Ph chromosome was present. A standard Ph translocation was detected in the cells obtained from the spleen, when the patient underwent splenectomy for treatment of the blastic crisis. Subsequent specimens obtained from the blood and bone marrow showed that the leukemic cells contained three clones: 45,XX, -9, -17, -22, +mar1, +mar2,9q+/46,XX, -17, +mar1,t(9;22)(q34;q11)/46,XX,t(9;22)(q34;q11). Cells with the "masked" Ph chromosome were thought to have been derived from the clone with the standard Ph translocation. We postulate that some variant Ph translocations, including those with a "masked" Ph chromosome, may be generated by a stepwise process following the genesis of a standard Ph translocation.

Human chromosome 22

The acrocentric chromosome 22, one of the shortest human chromosomes, carries about 52 000 kb of DNA. The short arm is made up essentially of heterochromatin and, as in other acrocentric chromosomes, it contains ribosomal RNA genes. Ten identified genes have been assigned to the long arm, of which four have already been cloned and documented (the cluster of lambda immunoglobulin genes, myoglobin, the proto-oncogene c-sis, bcr). In addition, about 10 anonymous DNA segments have been cloned from chromosome 22 specific DNA libraries. About a dozen diseases, including at least four different malignancies, are related to an inherited or acquired pathology of chromosome 22. They have been characterised at the phenotypic or chromosome level or both. In chronic myelogenous leukaemia, with the Ph1 chromosome, and Burkitt's lymphoma, with the t(8;22) variant translocation, the molecular pathology is being studied at the DNA level, bridging for the first time the gap between cytogenetics and molecular genetics.

The Philadelphia chromosome: a model of cancer and molecular cytogenetics

Recent developments in molecular biology related to the Ph chromosome lead us to an evaluation of knowledge regarding this chromosome. The molecular advances are related to two cellular oncogenes, c-abl and c-sis, and also to the identification and molecular cloning of specific areas of DNA (e.g., band 22q11), permitting the isolation of a probe specific for the translocation breakpoint domain. In the preponderant number of cases examined, it was found that the breakpoints at 22q11 occur within a limited region of up to 5-6 kb, for which the term "breakpoint cluster region" (bcr) has been suggested. In contrast, breaks at 9q34 seem to occur within a much larger region at the molecular level. Yet to be established is the exact genetic composition of the bcr and a determination as to whether or not the breaks leading to the disease occur preferentially within specific areas. In spite of this level of knowledge, we do not understand how the Ph chromosome participates in CML. If Ph-positive CML is ultimately associated with a cascade of gene activations, the unraveling of their nature and chronology will undoubtedly tell us much of their contribution to the biology of CML, in particular, and to neoplasia, in general. In this respect, the rather clear description of CML in cytogenetic, clinical, and laboratory terms, the relatively long chronic phase of the disease, and the association of the blastic phase with nonrandom chromosome changes (at least in the initial phases of the disease) make Ph-positive CML an excellent candidate for a model for the study of molecular events in human neoplasia.

The 14q+ marker in hairy cell leukaemia. A cytogenetic study of 15 cases

Leukaemic cells from 19 patients with hairy cell leukaemia (HCL), characterised by morphological, immunological and ultrastructural criteria, were investigated for chromosome abnormalities after stimulation with B-cell mitogens (Pokeweed mitogen (PWM), lipopolysaccharide B and EBV). The cells from all cases had a B-cell phenotype and in each case only a single light chain type was expressed on the membrane of the cells. Only 15 patients with adequate metaphases are included in this study. Clonal chromosome abnormalities were observed in 12 patients of which five had a 14q + involving q32. Of the remaining 3 cases 1 had nonclonal abnormalities and 2 had normal karyotypes. The donor chromosomes were identified in 3 cases and were found to be 9, 18 and 22. An interstitial rearrangement of chromosome 14 involving band q22 was seen in 2 cases and a deletion of chromosome 14 at q24 in 1 case. Amongst other chromosome abnormalities 12p was involved in 4 cases, 12q in 2 cases and chromosomes 7 and 22 in 3 cases each. The significance of the abnormalities has been discussed in relation to sites of cellular oncogenes. Our study demonstrates that chromosome abnormalities common to other B-cell disorders are present in HCL.

Translocation of c-abl to "masked" Ph in chronic myeloid leukemia

In two patients with chronic myeloid leukemia (CML), the nature of the chromosomal rearrangement giving rise to "masked" Ph has been studied by in situ hybridization of human c-abl sequences. The c-abl probes hybridized to the 22q11 region of the "masked" Ph, demonstrating that translocation of sequences from 9q34 to the Ph did occur exactly as in standard Ph or in other types of variants previously studied. These results provide additional evidence for the occurrence of a constant molecular rearrangement in Ph-positive CML.