The Philadelphia chromosome: a model of cancer and molecular cytogenetics

Activation of recombinational repair in Ewing sarcoma cells carrying EWS-FLI1 fusion gene by chromosome translocation

Chromosome translocation (TL) is an important mode of genomic changes underlying human tumorigenesis, the detailed mechanisms of which are, however, still not well understood. The two major modalities of DNA double strand break repair, i.e. homologous recombination (HR) and non-homologous end-joining (NHEJ), have been hypothesized. In a typical TL⁺ human neoplasm, Ewing sarcoma, which is frequently associated with t(11;22) TL encoding the EWS-FLI1 fusion gene, NHEJ has been regarded as a model to explain the disease-specific TL. Using comprehensive microarray approaches, we observed that expression of the HR genes, particularly of RAD51, is upregulated in TL⁺ Ewing sarcoma cell lines, WE-68 and SK-N-MC, as in the other TL⁺ tumor cell lines and one defective in DNA mismatch repair (MMR). The upregulated RAD51 expression indeed lead to frequent focus formation, which may suggest an activation of the HR pathway in these cells. Furthermore, sister chromatid exchange was frequently observed in the TL⁺ and MMR-defective cells. Intriguingly, ionizing irradiation revealed that the decrease of 53BP1 foci was significantly retarded in the Ewing sarcoma cell lines, suggesting that the NHEJ pathway may be less active in the cells. These observations may support an HR involvement, at least in part, to explain TL in Ewing sarcoma.

Monitoring Chronic Myeloid Leukemia: How Molecular Tools May Drive Therapeutic Approaches

More than 15 years ago, imatinib entered into the clinical practice as a "magic bullet"; from that point on, the prognosis of patients affected by chronic myeloid leukemia (CML) became comparable to that of aged-matched healthy subjects. The aims of treatment with tyrosine kinase inhibitors (TKIs) are for complete hematological response after 3 months of treatment, complete cytogenetic response after 6 months, and a reduction of the molecular disease of at least 3 logs after 12 months. Patients who do not reach their goal can switch to another TKI. Thus, the molecular monitoring of response is the main consideration of management of CML patients. Moreover, cases in deep and persistent molecular response can tempt the physician to interrupt treatment, and this "dream" is possible due to the quantitative PCR. After great international effort, today the BCR-ABL1 expression obtained in each laboratory is standardized and expressed as "international scale." This aim has been reached after the establishment of the EUTOS program (in Europe) and the LabNet network (in Italy), the platforms where biologists meet clinicians. In the field of quantitative PCR, the digital PCR is now a new and promising, sensitive and accurate tool. Some authors reported that digital PCR is able to better classify patients in precise "molecular classes," which could lead to a better identification of those cases that will benefit from the interruption of therapy. In addition, digital PCR can be used to identify a point mutation in the ABL1 domain, mutations that are often responsible for the TKI resistance. In the field of resistance, a prominent role is played by the NGS that enables identification of any mutation in ABL1 domain, even at sub-clonal levels. This manuscript reviews how the molecular tools can lead the management of CML patients, focusing on the more recent technical advances.

Characterization and targeting of neoplastic stem cells in Ph+ chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of an oncogenic fusion gene, BCR–ABL1. This fusion gene produces a cytoplasmic protein with tyrosine kinase activity that acts as a main driver of oncogenesis and abnormal proliferation of myeloid cells in CML. Targeted therapy with BCR–ABL1 tyrosine kinase inhibitors (TKIs) such as imatinib is followed by long-term responses in most patients. However, despite continuous treatment, relapses occur, suggesting the presence of TKI-resistant neoplastic stem cells in these patients. Here, we discuss potential mechanisms and signaling molecules involved in the prosurvival and self-renewal capacity of CML neoplastic stem cells as well as antigens expressed by these cells. Several of these signaling molecules and cell surface antigens may serve as potential targets of therapy and their use may overcome TKI resistance in CML in the future.

The nuclear translocation assay for intracellular protein-protein interactions and its application to the Bcr coiled-coil domain

Protein interactions are critical for normal biological processes and molecular pathogenesis. While it is important to study these interactions, there are limited assays that are performed inside the cell, in the native cell environment, where the majority of protein-protein interactions take place. Here we present a method of studying protein interactions intracellularly using one protein of interest fused to a localization-controllable enhanced GFP (EGFP) construct and the other protein of interest fused to the red fluorescent protein, DsRed. Nuclear translocation of the EGFP construct is induced by addition of a ligand, and the difference in nuclear localization between the induced and noninduced states of the DsRed construct provides an indication of the interaction between the two proteins. This assay, the nuclear translocation assay (NTA), is introduced here as broadly applicable for studying protein interactions in the native environment inside cells and is demonstrated using forms of the coiled-coil domain from the breakpoint cluster region (Bcr) protein.

Chronic myelogenous leukemia as a paradigm of early cancer and possible curative strategies

The chronological history of the important discoveries leading to our present understanding of the essential clinical, biological, biochemical, and molecular features of chronic myelogenous leukemia (CML) are first reviewed, focusing in particular on abnormalities that are responsible for the massive myeloid expansion. CML is an excellent target for the development of selective treatment because of its highly consistent genetic abnormality and qualitatively different fusion gene product, p210(bcr-abl). It is likely that the multiple signaling pathways dysregulated by p210(bcr-abl) are sufficient to explain all the initial manifestations of the chronic phase of the disease, although understanding of the circuitry is still very incomplete. Evidence is presented that the signaling pathways that are constitutively activated in CML stem cells and primitive progenitors cooperate with cytokines to increase the proportion of stem cells that are activated and thereby increase recruitment into the committed progenitor cell pool, and that this increased activation is probably the primary cause of the massive myeloid expansion in CML. The cooperative interactions between Bcr-Abl and cytokine-activated pathways interfere with the synergistic interactions between multiple cytokines that are normally required for the activation of stem cells, while at the same time causing numerous subtle biochemical and functional abnormalities in the later progenitors and precursor cells. The committed CML progenitors have discordant maturation and reduced proliferative capacity compared to normal committed progenitors, and like them, are destined to die after a limited number of divisions. Thus, the primary goal of any curative strategy must be to eliminate all Philadelphia positive (Ph+) primitive cells that are capable of symmetric division and thereby able to expand the Ph+ stem cell pool and recreate the disease. Several highly potent and moderately selective inhibitors of Bcr-Abl kinase have recently been discovered that are capable of killing the majority of actively proliferating early CML progenitors with minimal effects on normal progenitors. However, like their normal counterparts, most of the CML primitive stem cells are quiescent at any given time and are relatively invulnerable to the Bcr-Abl kinase inhibitors as well as other drugs. We propose that survival of dormant Ph+ stem cells may be the most important reason for the inability to cure the disease during initial treatment, while resistance to the inhibitors and other drugs becomes increasingly important later. An outline of a possible curative strategy is presented that attempts to take advantage of the subtle differences in the proliferative behavior of normal and Ph+ stem cells and the newly discovered selective inhibitors of Bcr-Abl. Leukemia (2003) 17, 1211-1262. doi:10.1038/sj.leu.2402912

Analysis of Philadelphia chromosome-negative BCR-ABL-positive chronic myelogenous leukemia by hypermetaphase fluorescence in situ hybridization

BACKGROUND

In 5%-10% of patients with of chronic myelogenous leukemia (CML), the Philadelphia chromosome (Ph) is not identified, despite the presence of the associated BCR-ABL molecular abnormality (Ph-negative, BCR-ABL-positive CML) because of sub-microscopic rearrangements.

PATIENTS AND METHODS

Six patients with Ph-negative, BCR-ABL-positive CML were investigated. The Ph chromosome detection via fluorescence in situ hybridization after 24-hour mitotic arrest of bone marrow cultures resulting in several hundreds of metaphases (hypermetaphase FISH or HMF) was useful in explaining the nature of the six cases.

RESULTS

Four patients had a low frequency of Ph-positive cells by HMF (5.7%, 4.8%, 3.9%, 0.2%), i.e., a typical Ph translocation. However, two cases involved a 9q34 inserted into chromosome 22q11 (74.2% and 92%), without a deletion from chromosome 22 and reciprocal translocation onto 9, i.e., not a typical Ph translocation. The pattern of UBCR gene rearrangement was characterized by the same genomic recombination of 5-BCR and c-ABL, both in the four cases of typical translocation (9;22) and in the two cases of insertion of 9q34 into chromosome 22q11.

CONCLUSIONS

The HMF identified two different bases for Ph-negative, BCR-ABL-positive cells in CML-presence of low frequency of cells with typical Ph translocations or presence of cells with ABL insertions into the BCR gene on chromosome 22.

Value of fluorescence in situ hybridization for detecting the bcr/abl gene fusion in interphase cells of routine bone marrow specimens

Fluorescence in situ hybridization (FISH) is a new technique that allows demonstrating of the bcr/abl gene fusion in bone marrow cells of patients with Philadelphia translocation (Ph)-positive chronic myeloid leukemia (CML). In this study, bone marrow samples of 150 patients were investigated routinely by interphase FISH, cytogenetics, and bone marrow histopathology. In 20 patients with reactive hyperplasia of the granulopoiesis and normal karyotypes, FISH revealed nonspecific bcr/abl fusion signals at a mean frequency of 2.7% of the cells examined. The cutoff level for specific fusion signals was set at three times the standard deviation (9.0%). None of the 29 cytogenetically Ph-negative patients with myeloproliferative disease other than CML had fusion signals exceeding 9%. The mean frequency of specific fusion signals in nontreated patients with CML (n = 59) was 92.7%, and 49.3% in patients with CML who received therapy (n = 42). For diagnosing Ph-positive CML, interphase FISH has been faster, more reliable, and more sensitive than cytogenetics, which was successful in 54 of 59 patients investigated at first diagnosis but only in 27 of 42 patients receiving therapy, and it failed to detect Ph-positive cells in three patients with CML. However, small percentages of less than 9.0% of cells with bcr/abl fusion signals were below the threshold of interphase FISH, thereby limiting its use for detecting minimal residual disease.

Fluorescence in situ hybridization (FISH) is a reliable diagnostic tool for detection of the 9;22 translocation

The fluorescence in situ hybridization (FISH) technique for detection of the 9;22 translocation was compared with the "gold standard" of conventional cytogenetics. For this purpose, both methods were applied to 81 bone marrow aspirates and/or peripheral blood specimens comprising 50 CML cases and controls from 31 patients without CML. Independently, core biopsies of these 81 patients were investigated by three histopathologists. Conventional karyotype analysis from unstimulated bone marrow cells was successful in 71/81 cases and demonstrated the Ph-chromosome in 42/46 CML patients. With FISH, results were obtained in all 81 cases investigated, confirming fusion of the ber and abl genes in all cytogenetically Ph-positive patients. Among the five Ph-chromosome-negative specimens bcr/abl fusions were detected in only one patient. The percentage of cells found to be Ph-positive by both methods was correlated, but in individual cases considerable differences in the numbers of Ph-positive cells were observed. Different results may be due to selection of cells after in vitro cultivation predominantly. FISH proved to be a very reliable technique for specimens that do not contain dividing cells. With FISH, large numbers of cells can easily be scored which is an advantage compared to conventional cytogenetics. Therefore, this method is particularly suitable for those whose therapy is being monitored or a relapse is suspected. However, the FISH results should be evaluated critically with respect to the practical limit of sensitivity since non-specific fusion signals can also be observed in a small percentage of cells in non-CML cases. It is suggested that each laboratory define its own threshold of bcr/abl fusion signals for diagnosing Ph-positive CML by FISH.

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.

New translocations [t(6;15)(p25;q22) and t(6;19)(q16;q13.3)] with t(9;22)(q34;q11) in a Ph-positive chronic myelogenous leukemia

A case with typical features of chronic myelogenous leukemia (CML) with two complex aberrations in addition to the standard t(9;22) is reported. Cytogenetic evaluation of the patient's bone marrow cells (BMC) showed 46,XX,t(6;19)(q16;p13.3),t(9;22)(q34;q11) in 60% of the mitotic cells and 46,XX,idem, t(6;15)(p25;q22) in the remaining 40% dividing cells. The patient's peripheral blood smear exhibited the usual differential observed in chronic-phase CML and was clinically indistinguishable from patients with the t(9;22) as the only translocation. We performed Southern blotting on BglII-digested DNA with the Trans-Probe (OSI) and in addition to the 4.8-, 2.3-, and 1.1-kilobase (kb) germline fragments, we detected an additional fragment at 7 kb. This probe spans the entire 5.8-kb M-breakpoint cluster region (BCR), and a single breakpoint in this region will appear as either one or two additional fragments. Because only one additional fragment was observed, both cell lines apparently share the same breakpoint in the ABL/BCR gene. Apparently the second aberrant cell line with the additional t(6;15) represents clonal evolution of the original abnormal clone.

Deletion of chromosome 22 without bcr rearrangement and without juxtaposition of c-abl in a case of acute myeloid leukemia

We describe a patient with acute myeloid leukemia (AML) who had a deletion of chromosome 22 at q11 as a sole chromosomal abnormality, resulting in the karyotype 46,XY,del(22)(q11). Southern blot analysis showed no bcr rearrangement and fluorescence in situ hybridization indicated no juxtaposition of c-abl. This study indicates that molecular events other than bcr rearrangement and c-abl juxtaposition were involved in leukemogenesis in this patient. We hypothesize that a tumor suppressor candidate gene may be located on the long arm of chromosome 22; its loss may lead to malignant transformation.

Cancer in the elderly

This article reviews geriatric oncology and assesses options for treatment and care of the elderly patient with cancer. The size of the population over 65 years old is defined, with particular reference to the continuing growth of this subsection of the community. The high incidence of many cancers and their associated mortality rates in the elderly are identified and the epidemiology of such diseases in the geriatric population is addressed. Given the discrepancies in incidence and survival rates between patients younger and older than 65 years, the association between tumorigenesis and the aging process is explored. Specific aspects of tumor growth in the elderly are considered. General considerations of therapy for elderly patients with cancer are discussed, including the pharmacokinetics and pharmacodynamics of chemotherapy in those over 65 years old, surgical options, the use of radiotherapy, and overall patient assessment. Next, treatment options for individual cancer states are reviewed, with particular emphasis on newer treatment options designed specifically for the elderly. Sections on cancer screening and supportive care are also included, the latter dealing with aspects of symptom control, quality of life assessment, and the physical and psychologic rehabilitation of the elderly patient with cancer who is undergoing treatment. Conclusions are then drawn as to the extent of the oncological process in those over 65 years old, with particular emphasis on the underdiagnosis and undertreatment of many malignancies in the past. The challenge created by the growing elderly population is underscored and necessary plans of action for oncologists in the future are defined. Such proposals are necessary if inroads are to be made into the unacceptable morbidity and mortality rates borne by our elderly patients with cancer.

The complete coding sequence of arg defines the Abelson subfamily of cytoplasmic tyrosine kinases

We have previously described partial genomic sequences of arg, a human gene related to c-abl, and shown that it is expressed as a 12-kilobase transcript and is located at chromosome position 1q24-25. In this study we elucidate the complete coding sequence of arg by characterization of cDNA clones. Analysis of the predicted amino acid sequence of arg revealed that it is indeed closely related to that of c-abl. The two proteins are strikingly similar with regard to overall structural architecture as well as the amino acid sequences of their tyrosine kinase and src homologous 2 and 3 domains. In addition, arg, like c-abl, is expressed as two transcripts that result from a process of alternative splicing and encode alternative protein forms that differ only in their amino termini. The two genes define the Abelson subfamily of cytoplasmic tyrosine kinases and share a common homolog in Drosophila.

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.

Seven variants including four new Philadelphia translocations

This paper reports on seven atypical Philadelphia chromosome translocations in chronic myelocytic leukemia. Three of them, a t(16;22), t(17;22), and t(9;14;22) have already been observed before, while the t(X;9;11;22), t(X;22), t(3;22) and t(3;4;9;22) are newly reported.

Lineage non-specific down regulation of P210bcr/abl in the CML cell line, KU-812-F, during differentiation

CML cell line, KU-812-F, originally established from a patient with Philadelphia-chromosome-positive chronic myelocytic leukemia has maintained the ability to differentiate into both granuloid (basophilic) and erythroid lineages. The expression of P210bcr/abl in KU-812-F cells during differentiation was studied by immunoblotting and immunoprecipitation. Immunoblotting with anti-phosphotyrosine sera revealed the down-regulation of P210bcr/abl in both granuloid and erythroid lineages. Immunoprecipitation with anti-abl antibodies of 35S-methionine-labelled cells revealed a reduced rate of synthesis of P210bcr/abl protein. Cytotoxic agents that caused growth inhibition of the cells did not alter the expression of P210bcr/abl. These results indicate that the down regulation of P210bcr/abl protein is a lineage non-specific event accompanied by differentiation.

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.

Involvement of bands 9q21-q22 in five cases of acute nonlymphocytic leukemia

Five patients with acute nonlymphocytic leukemia (ANLL) with chromosomal aberrations involving bands 9q21-q22 are described. The abnormalities were an interstitial deletion in two cases of ANLL FAB type M4 and M4 with eosinophilia, a terminal deletion in two cases of M4 and M5 type ANLL, and a translocation in an M2 ANLL. A review of reported cases of ANLL with abnormalities of chromosome 9 revealed a clustering of breaks at the region 9q21-q22, suggesting a possible role for these bands in leukemogenesis.

Philadelphia-positive thrombocythemia with a complex translocation involving chromosomes 9, 15, and 22

We report a case of Philadelphia chromosome (Ph) positive thrombocythemia with a complex translocation. G-banding analysis showed the predominant karyotype to be 46,XX,t(9;15;22). Southern blot analysis revealed a rearrangement within the breakpoint cluster region on chromosome 22 similar to findings in chronic myeloid leukemia. These data suggest the presence of a complex Ph translocation involving t(9;15;22)(q34.1 or q34.3;q26.1;q11 or q13).

Cytogenetic and molecular studies in primary myelofibrosis

Cytogenetic and molecular data of three patients affected by primary myelofibrosis with myeloid metaplasia (PMMM) evolving to blastic crisis are reported. The cytogenetic findings were uncommon. The first patient (female) showed an idic(X)(q13) as the sole alteration in chronic phase, with an additional r(7) in 67% of the cells of the blast crisis; the other two patients showed, in blast crisis, a partial trisomy of the long arm of chromosome 1, without translocation, as a unique structural abnormality. These findings confirm the presence of nonrandom, although nonspecific, alterations in PMMM that, in our cases, seem to be related to the multistep progression of the neoplastic process. Molecular investigations have been applied to study the genomic organization and the level of expression of genes such as bcr and calcyclin and c-fms protooncogene possibly involved in the molecular mechanisms underlying cell proliferation in hematopoietic cells. The data obtained are discussed with respect to the myeloproliferative disorder.

Molecular analysis of the bcr rearrangement in a case of Ph'-negative blastic crisis of Ph'-positive chronic myelogenous leukemia

We describe here a patient with Ph'-positive chronic myelogenous leukemia (CML) who developed a Ph'-negative blastic crisis. The blast DNA was analyzed on two different occasions, at the beginning of the blastic phase and at the end, shortly before the patient's death. Although cells from both samples had no Ph' chromosome marker (not even a masked one) we could detect a rearrangement of the bcr gene in the second DNA sample, using a '3'-bcr' probe. The same probe and a '5'-bcr' probe failed to detect any rearranged band in the first DNA sample. No rearrangement was identified at the c-myc and N-ras loci, while a slight c-myc amplification was evident in both DNA samples tested.

Deletion of c-ets1 and T3 gamma loci from the 11q- chromosome in the human monoblastic cell line U937

The 11q- chromosome in the human monoblastic cell line U937 appears to be derived from an interstitial deletion in bands 11q21-23/24 or a translocation with an unknown chromosome. We show here by in situ hybridisation that this chromosome has lost the c-ets1 and T3 gamma loci. C-ets1 and T3 gamma sequences were not detected on any chromosomes besides the normal 11, indicating either that they were lost from the genome or that the chromosome to which they were translocated was not present in a high enough proportion of the cells to be detected by in situ hybridisation. No DNA rearrangements were found with three different restriction enzymes in the c-ets1, N-CAM, Thy-1 and c-sea genes detected by our probes. There was also no detectable rearrangement in the c-fms gene which was shown to be translocated from chromosome 5 to chromosome 1 in a subline of U937. The size of the c-fms and c-ets1 messages were normal. The possible significance of these findings is discussed.

A new translocation involving chromosomes 8 and 9 in a Philadelphia-negative chronic myelogenous leukemia

A new case is presented displaying typical features of the stable phase of chronic myelogenous leukemia (CML), with a complex translocation involving chromosomes 8q and 9q. Cytogenetic evaluation revealed an abnormal karyotype, 46,XY,t(8;9)(q22;q34). Both chromosomes 22 were found to be cytogenetically normal. After molecular evaluation the cytogenetic diagnosis was revised to 46,XY,t(8;9;22)(q22;q34;q11). The importance of the chimeric abl/bcr gene fusion product in the pathogenesis of CML is suggested as a characteristic feature, even in some patients with a so-called Philadelphia (Ph) negative CML. Utilization of molecular probes in the evaluation of such cases must become a routine diagnostic procedure. Our patient received the potential benefit of Ph-positive directed therapy because of the present approach.

A t (11;21) (13;q22) in Ph-positive chronic myelogenous leukemia

Reciprocal translocations, in addition to that of the Ph chromosome, though rare, have been reported in chronic myelogenous leukemia (CML). We describe here a case of Ph-positive CML with a new translocation, t (11;21) (q13;q22), and missing Y, which were present both during transformation to the blastic crisis and in the subsequent reversion to the chronic phase. The possible significance of this abnormality is discussed.

Possible cytogenetic distinction between lymphoid and myeloid blast crisis in chronic granulocytic leukemia

This study consists of 25 patients with chronic granulocytic leukemia in blast crisis (BC) or with acute leukemia who had a Ph1 chromosome and one or more other chromosome abnormalities and who were investigated by cytochemistry and immunocytochemistry techniques to determine whether the predominant blasts were myeloid or lymphoid. The disorder was myeloid in 15 patients, lymphoid in 8, and mixed in 2. Among the 15 patients with myeloid disorders, 13 (86.6%) had an additional Ph1 chromosome, i(17q), +8, +19, or some combination of these abnormalities. None of the eight patients with a lymphoid disorder had +8, +19, or i(17q), but one had an additional Ph1 chromosome. Among the eight patients with lymphoid disorders, two had structural abnormalities of chromosome 7 and two were monosomy 7. None of the patients with myeloid disease had a structurally abnormal chromosome 7, but one was monosomy 7. Our findings suggest that the number of chromosomes in an abnormal clone may be unreliable for distinguishing between lymphoid and myeloid BC. Most patients with myeloid disease had only abnormal metaphases, whereas many patients with lymphoid disorders had both normal and abnormal metaphases. This finding may partially explain why many patients with lymphoid BC respond better to treatment than do those with myeloid BC.

Duplication of Ph and of 9q+ chromosomes during the blastic transformation of a CML case

We describe the blastic transformation of a case of chronic myelocytic leukemia in which, among other abnormalities, one extra Philadelphia and one extra 9q+ were observed. Molecular studies and analysis of the clonal evolution of the karyotype led to the interpretation of such an unusual finding as the result of nondisjunction, rather than of a double t(9;22) translocation.

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.

Genomic diversity of Philadelphia-positive chronic myelogenous leukemia

The incidence of breakpoints in CML patients with variant translocations was investigated. There was no relationship between the length of various chromosomes with breakpoint frequency. However, a significantly higher (p less than 0.05) incidence of breaks were seen on the long arms as compared to the short arms due mainly to the involvement of 9q and 22q in these translocations. Chromosome 17 showed a significantly (p less than 0.005) higher involvement in these translocations, however only when 9q34-qter was not cytogenetically involved. A total of 683 breaks were found in 225 cases. 362 of these were located at c-abl and c-sis, while 110 were at other oncogenetic sites. The prognostic and hematologic features of patients with variant translocations are not significantly different from those of CML cases with the typical 9q;22q translocation. Some of these complex translocation, where the breakpoints are correlated with oncogenetic sites, are further discussed in molecular terms.

Overlapping cDNA clones define the complete coding region for the P210c-abl gene product associated with chronic myelogenous leukemia cells containing the Philadelphia chromosome

The Philadelphia chromosome, observed in greater than 90% of patients with chronic myelogenous leukemia, results from a reciprocal translocation between chromosomes 9 and 22. The translocation breakpoint on chromosome 9 occurs near the ABL gene and correlates with the production of a chronic myelogenous leukemia-specific 8.5-kilobase ABL-related mRNA species accompanied by a structurally altered ABL protein (P210c-abl). The N-terminal sequence of the protein is derived from the BCR gene on chromosome 22. We have isolated overlapping cDNA clones from the K-562 cell line corresponding to approximately 8.5 kilobases of mRNA and have sequenced 2550 nucleotides at the 5' end. Our results indicate that the 5' end of the 8.5-kilobase mRNA consists of greater than 400 nucleotides of noncoding sequence that are greater than 80% G + C rich. Based on our sequence analysis, we propose that initiation of translation occurs at nucleotide 471, such that the initial 927 amino acids of P210c-abl are derived from BCR sequences. Our cDNA clones thus define the complete coding sequences for the P210c-abl gene product.