Genomic diversity of Philadelphia-positive chronic myelogenous leukemia

[The molecular-cytogenetic characterization and tyrosine kinase inhibitors efficacy in newly diagnosed chronic phase CML patients with variant Philadelphia chromosomes]

Objective: To investigate the molecular-cytogenetic characterization and impact on tyrosine kinase inhibitors (TKIs) therapy in chronic phase of chronic myeloid leukemia (CML-CP) patients with variant Ph chromosome (vPh). Methods: The clinical data of 32 patients with vPh chromosomes were collected and compared with 703 patients with typical Ph chromosome in newly diagnosed CML-CP who were on first-line imatinib (IM) and with BCR-ABL transcript of P210. Results: There was no significant difference in demographic and hematological characteristics between vPh and classic Ph patients. 3(9.4%) of the 32 vPh cases were simple variant translocations. Among the remaining 29 cases with complex variant translocations, 28 cases (87.5%) involved 3 chromosomes, and only 1 (3.1%) involved 4 chromosomes. Except for 8, 15, 18, X, and Y chromosomes, the other chromosomes were involved. The frequency of chromosome 12q(15.5%) and 1p (12.1%) were higher involved. The most common FISH signal pattern was 2G2R1Y (74.1%), followed by 1G1R2F (14.8%), 2G1R1Y (3.7%), 1G2R1Y (3.7%), 1G1R1Y (3.7%). The comparison of complete cytogenetic response (CCyR) (P=0.269), major molecular response (MMR) (P=0.391) were carried out between simple and complex mechanisms, without difference. Compared with the classic Ph, the patients with vPh had higher IM primary resistance rate (χ2=3.978, P=0.046), especially primary hematological resistance (χ2=7.870, P=0.005), but the difference of CCyR (χ2=0.192, P=0.661), MMR (χ2=0.822, P=0.365), EFS (χ2=0.509, P=0.476), OS (χ2=3.485, P=0.062) were not statistically significant, and multivariate analysis showed that the presence of vPh did not affect OS (RR=0.692, 95%CI 0.393-1.765, P=0.658)、EFS (RR=0.893, 95%CI 0.347-2.132, P=0.126) and PFS (RR=1.176, 95%CI 0.643-2.682, P=0.703). Conclusion: CML-CP patients with vPh and classic Ph had similar demographic and hematological characteristics. Except for 22q11, 9q34, the frequency of chromosome 12q and 1p were higher involved. The most common FISH signal pattern was 2G2R1Y, and different mechanisms had no impact on TKIs therapy. Compared with cases with classic Ph chromosomes, the patients with vPh chromosomes had higher risk of IM primary resistance, especially primary hematological resistance, which can obtain deeper molecular response quickly after changing to second-generation TKIs and didn't affect long-term outcomes and OS.

Characterization of a complex translocation [t(4;9;22)(p16;q34;q11)] in chronic myelogenous leukemia by fluorescence in situ hybridization technique

A patient was referred with a high leukocyte count and diagnosed with chronic myelogenous leukemia (CML). Although practically asymptomatic since the time of diagnosis, he had a variable and inconsistent response to treatment. All of his bone marrow cells had a complex, three-way translocation, involving chromosomes 4, 9 and 22. Translocation of chromosome 4 to chromosome 9 was undetectable by routine cytogenetic techniques; however, by the fluorescence in situ hybridization technique, a three-way translocation was identified, 46,XY,t(4;9;22)(p16;q34;q11). Although, other chromosomes are frequently involved in complex or variant translocations with chromosome 9 and 22, participation of chromosome 4 is a very rare event. So far, two previous cases have been described in the literature with translocations involving chromosome 4p16. We present a third case of CML having similar break points whose clinical presentation is unusual.

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.

Direct visualization of the transposed ABL gene in a duplicated masked Ph chromosome

In a small percentage of cases of chronic myelogenous leukemia (CML), where the Ph chromosome is masked because of highly complex translocations and sub-microscopic rearrangements, precise identification of chromosomal aberrations by routine banding techniques has been difficult. We report on a new case of CML in which a single copy of a masked Ph chromosome was duplicated during blast crisis, i.e., the karyotype was 47,XY,dir ins(22;9)(q11;q34.1q34.2),t(1;22) (q21;q11), + der (22)t(1;22)(q21;q11). The chromosome in situ suppression hybridization (CISS) technique with whole chromosome 1 and 22 specific painting probes demonstrated that 22q11-qter had been translocated to 1q21, whereas 22q11 was the recipient of 1q21-qter. Furthermore, a cosmid probe identified the location of the ABL gene on only one chromosome 9 (band q34). The other ABL gene could be detected on both derivative chromosomes 22 at band q11 which was flanked by the translocated part of the long arm of chromosome 1, thus providing direct visualization of the ABL insertion in a double masked Ph chromosome. A breakpoint within the 5.8 kb major breakpoint cluster [M-BCR] region was shown by Southern blotting.

Disappearance of a highly unusual clone, 46,XY,del(7)(p12),t(9;22)(q34;q11) in chronic myeloid leukemia after treatment with recombinant interferon and cytosine arabinoside

A patient with the typical features of the stable phase of chronic myeloid leukemia (CML) displayed two karyotypically related subclones. In addition to the t(9;22), cells from one clone contained a deletion of the short arm of chromosome 7, del(7)(p12), [46,XY,del(7)(p12),t(9;22)(q34;q11)]; the other contained only the standard translocation [46,XY,t(9;22)(q34;q11)]. Cells with a deletion of the short arm of chromosome 7 at band p12 as the only additional abnormality have not been observed previously in CML. Conventional chemotherapy with hydroxyurea and then with recombinant interferon-alpha (rIFN-alpha) did not reduce the population of either subclone. However, after treatment with a combination of rIFN-alpha and low-dose cytosine arabinoside (LoDac) continuously infused subcutaneously (s.c.), cells from the clone with the deleted chromosome 7 disappeared and normal metaphases were demonstrable.

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.

On the topology of normal chromatids and on their translocations in myelogenous leukemia

After some comments on the topology of chromatids, restructuring of the interphase nucleus is conjectured to depend upon the nuclear vesicle apparatus. These vesicles change the intrinsic shape of chromatids to fit the different topology of the interphase nuclear spheroid. Reciprocal translocations between selected chromatids result whenever the nucleus of malignant cells organizes de novo certain exceptional or emergency differentiation paths. However, the almost unavoidable chimeric genes resulting from these translocations may be less ominous than hitherto suspected. This seems to be the case for chronic myelogenous leukemia, where the bcr-abl chimeric gene lessens the aggressiveness of the primary clone when functioning in the context of myelomonocitic differentiation. Finally, our model estimates the statistical incidences of the bcr-abl chimera. These estimates are found to agree with clinical data better than evaluations from the random mutation theory.

Location of breakpoints within the major breakpoint cluster region (bcr) in 33 patients with bcr rearrangement-positive chronic myeloid leukemia (CML) with complex or absent Philadelphia chromosomes

We report the sublocalization of the breakpoint in chromosome 22 in 33 patients with chronic myeloid leukemia (CML) who also had unusual marrow cytogenetics. In 23 patients, the leukemic clones were characterized by Philadelphia (Ph1) chromosomes that arose through complex translocations that involved three or more chromosomes. In the remaining ten patients, there were no detectable Ph1 chromosomes despite molecular evidence for the presence of rearrangements in the major breakpoint cluster region (bcr) of chromosome 22 in all cases. There was no significant difference between the two groups with respect to location of the breakpoints within the bcr. When these two groups of patients were combined, there was a significant excess of breakpoints in one segment of the bcr when compared to the distribution of breakpoints seen in 119 patients with simple 9;22 translocations. The difference in breakpoint distributions did not appear to be entirely attributable to differences between groups in disease duration at the time of study. These data support the notion that the unusual genetic recombinations that give rise to BCR/ABL fusion genes in CML involve specific DNA sequences of BCR (and possibly ABL) and additional, recombinogenic sequences, at least some of which are present in loci known to be nonrandomly involved in complex Ph1 translocations.

Two new chromosomal abnormalities in chronic myelogenous leukemia 46,XY,t(9;15;22)(q34;q22;q11) and 46,XY,t(6;9;12;22)(p21;q34;q24;q11)

Two new variant cases of chronic myelogenous leukemia (CML) are presented. The first case is a 19-year-old male with a 46,XY,t(9;15;22)(q34;q22;q11) karyotype. The second case is a 75-year-old man with a 46,XY,t(6;9;12;22)(p21;q34;q24;q11) karyotype. In both cases, the prognosis was no different from those cases of CML with the standard t(9;22) as the only abnormality. We recommend that all unusual translocations be reported.

Clonal expansion after bone marrow transplantation in a patient with chronic myelogenous leukemia

A patient with chronic myelogenous leukemia (CML) having the standard [t(9;22), Ph] translocation is presented where the Philadelphia (Ph) chromosome disappeared following bone marrow transplantation (BMT). The Ph chromosome reappeared in host cells after one year of stable hematologic remission. Three additional cell lines, all possessing the Ph chromosome with other abnormalities were consistently present in her marrow cells. Two years after BMT, ninety percent of her dividing bone marrow cells had become leukemic. The patient's clinical status remains unchanged, despite complex cytogenetic findings. The high incidence of multiple aberrant leukemic clones present in this case remains intriguing. Possible mechanisms for this unique transformation after BMT are 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.

Chromosome abnormalities in CML

The Ph chromosome is the hallmark of CML, where it is found in more than 90% of the cases. Cytogenetically, it usually results from a t(9;22)(q34;q11). The Ph arises in a stem cell and in chronic phase is found in all haematopoietic cell lineages, although it causes only increased granulopoiesis, and sometimes increased thrombopoiesis; furthermore blast crisis may occur in all differentiative patterns of the pluripotent stem cell. Recently, molecular investigations of Ph positive CML cases have revealed a consistent genomic recombination between two genes, BCR on chromosome 22 and the ABL oncogene. The latter is translocated from 9q34, its normal site, to the 22q- or Ph chromosome. This molecular rearrangement expresses a unique 8.5 kb BCR-ABL hybrid mRNA transcript, that encodes an altered BCR-ABL protein of approximately 210 kD with enhanced in vitro tyrosine kinase activity. The breakpoints on chromosome 22q- are clustered in a 5 kb DNA fragment, allowing their study using Southern blot analysis. Cytogenetic variant forms of the Ph translocation involving three or more chromosomes are found in about 5% of the cases. Southern blot and in situ hybridization studies have demonstrated that these variants are cytogenetically more complex than the standard t(9;22) but molecularly they show the same essential genomic recombination. This is also true for a small number of cases of Ph negative CML. Clonal progression, indicated by the presence of clonal, non-random chromosome abnormalities, in addition to the Ph is rare during chronic phase but is found in 80% of blast crisis. These additional aberrations may precede BC by weeks or months and have therefore a clear prognostic value. Ph is not restricted to CML, since it is also found in ALL (20% of adult cases) and rarely in AML. Ph in acute leukaemia is cytogenetically indistinguishable from Ph in CML, but molecular studies have shown that in 50% of the cases the breakpoint on chromosome 22 is different from the very consistent and characteristic breakpoint in CML. Nevertheless genomic recombination takes place that results in a novel ABL protein at least in some of the cases. Despite extensive cytogenetic and molecular investigations, the mechanisms underlying the formation of the Ph as well as the pathogenesis of Ph positive CML are still unknown but are now the object of intensive research.