Cytogenetic studies in 56 cases with Ph1-positive hematologic disorders

NPM1 Mutated, BCR-ABL1 Positive Myeloid Neoplasms: Review of the Literature

Breakpoint cluster region - Abelson (BCR-ABL1) chimeric protein and mutated Nucleophosmin (NPM1) are often present in hematological cancers, but they rarely coexist in the same disease. Both anomalies are considered founder mutations that inhibit differentiation and apoptosis, but BCR-ABL1 could act as a secondary mutation conferring a proliferative advantage to a pre-neoplastic clone. The 2016 World Health Organization (WHO) classification lists the provisional acute myeloid leukemia (AML) with BCR-ABL1, which must be diagnosed differentially from the rare blast phase (BP) onset of chronic myeloid leukemia (CML), mainly because of the different therapeutic approach in the use of tyrosine kinase inhibitors (TKI). Here we review the BCR/ABL1 plus NPMc+ published cases since 1975 and describe a case from our institution in order to discuss the clinical and molecular features of this rare combination, and report the latest acquisition about an occurrence that could pertain either to the rare AML BCR-ABL1 positive or the even rarer CML-BP with mutated NPM1 at the onset. Differential diagnosis is based on careful analysis of genotypic and phenotypic features and anamnestic, clinical evolution, and background data. Therapeutic decisions must consider the broader clinical aspects, the comparatively mild effects of TKI therapy versus the great benefit that might bring to most of the patients, as may be incidentally demonstrated by our case history.

BCR/ABL fusion gene detected on 9q34 by fluorescence in situ hybridization in an acute leukemia with two BCR/ABL positive clones, one Ph-negative and one Ph-positive

We report cytogenetic, fluorescence in situ hybridization (FISH), and molecular analyses in the first reported case of an acute leukemia with two BCR-positive clones: one cell Ph-positive and all others Ph-negative. A BCR/ABL fusion gene on 9q34 was detected only with a BCR/ABL dual color translocation probe. These FISH interphase signals must be confirmed on a metaphase to avoid an erroneous interpretation. This observation appears to indicate a 2-step mechanism for this aberrant fusion gene localization: first, a classical t(9;22), and then the transfer of the fusion gene formed on chromosome 22 to chromosome 9 by a second translocation between the long arms of the derivative chromosomes 9q+ and 22q-, masking the first chromosome exchange.

Tetrasomy 8 as a primary chromosomal abnormality in a child with acute megakaryoblastic leukemia

Tetrasomy 8 is a relatively rare chromosomal abnormality in hematological disorders, and is mostly associated with myeloid malignancies and poor prognosis. In a number of cases, tetrasomy 8 has been reported as an accompanying anomaly with other chromosomal changes. In this report, we describe a 14-year-old girl with acute megakaryoblastic leukemia associated with tetrasomy 8 (primary) and trisomy 6, 19 and 20. She died 6 months after diagnosis, suggesting a relatively poor prognosis for AML with tetrasomy 8. To the best of our knowledge, this is the first report of a tetrasomy 8 abnormality associated with subtype FAB M7. Interestingly, this abnormality has not been previously reported in childhood AML patients.

A FISH study of variant Philadelphia rearrangements

A total of 39 variant Philadelphia (Ph) translocations were studied by fluorescence in situ hybridization (FISH) using MBCR/ABL, mBCR/ABL, or DBCR/ABL probes. Seven cases did not have a BCR/ABL fusion signal. Of a total of 32 fusion-positive cases, 5 were simple variants involving chromosome 22 and another chromosome apart from chromosome 9; 23 were complex variants involving chromosomes 22, 9, and a third chromosome (18 cases), or 22, 9, and two other chromosomes (4 cases). Masked Ph rearrangements were detected in 4 cases. One case was a Ph chromosome mimic. Fluorescence in situ hybridization has become a widely used method for studying Ph rearrangements. The latest probe that is being used is the DBCR/ABL (double reciprocal BCR/ABL signals). The expected pattern for this probe is one green ABL signal (1G) on the normal 9, one red BCR signal (1R) on the normal 22, and two fusion signals, BCR/ABL and ABL/BCR (2F), on a derivative 22 and a derivative 9, respectively. Deviant patterns from 1G1R2F, and sometimes 1G1R2F, were indicative of a variant, as long as there was a fusion signal. However, in interphase analysis, it is not possible to visualize a variant rearrangement, and when a deviant pattern involving at least one fusion signal is observed, the following possibilities should be contemplated. The different patterns observed in fifteen Ph variants are described. The patterns observed in variants studied with the DBCR/ABL probe were 2G2R1F (40%), 1G1R2F (20%), 1G1R1F (20%), 1G2R1F (13.3%), and 2G1R1F (6.66%). A single mechanism is involved in the formation of each of these patterns. A 2G2R1F, FISH pattern in 6 cases appears to involve a single concerted event of simultaneous breaks on the participating chromosomes followed by mismatched joining. The three cases with 1G1R2F most probably arose by two sequential rearrangements. The 1G1R1F pattern suggests that either the BCR and ABL breakpoints are different, or there are deletions at the breakpoints, because residual signals are not observed. Two independent events appear to be involved in 1G2R1F with a reverse cryptic 9,22 rearrangement as the first event. In one case of 2G1R1F, the plausible explanation is an insertion of ABL next to BCR and either a simultaneous or a sequential translocation with another chromosome.

Isolated tetrasomy 8 in minimally differentiated acute myeloid leukemia (AML-M0)

Tetrasomy 8 as a sole anomaly in hematological disorders is relatively rare. To the best of our knowledge, only 19 such cases have been described in the literature to date. Of them, acute myeloid leukemia (AML) in 13 (M1, one; M2, three; M4, one; M5, eight), acute lymphoblastic leukemia(ALL) in one, myelodysplastic syndrome(MDS) in 3, polycythemia vera(PV) and myelofibrosis(MF), one case each. Their median survival was 20 weeks. Here, we report the first case of a 29-year-old man with minimally differentiated AML (AML-M0) displaying a tetrasomy 8 clone. Immunophenotyping showed positivity with CD33, CD34 and intracellular MPO, but all lymphoid markers tested were negative. Conventional cytogenetics of bone marrow cells showed 84.9% of metaphases with tetrasomy 8 in addition to 15.1% with normal diploidy. However, Fluorescence in situ hybridization(FISH) using a centromeric probe specific for chromosome 8 revealed trisomy 8 in 14.2% of interphase nuclei besides tetrasomy 8 in 82.4%. The patient died four weeks after diagnosis without therapy. In conclusion, these findings suggest that tetrasomy 8 is associated with a heterogeneous group of myeloid disorders and heralds a bad prognosis. It may be a consequence of clonal evolution of trisomy 8.

Pentasomy 8q in myelodysplasia

Trisomy 8 and, less commonly tetrasomy 8, are karyotypic aberrations found in myeloid malignancies. We describe a unique case of acute myeloid leukemia with partial pentasomy 8 resulting from duplication of isochromosome 8q, and discuss its possible roles in leukemogenesis.

Tetrasomy 8 detected by interphase cytogenetics in a child with acute lymphocytic leukemia

Tetrasomy 8 is a rare clonal anomaly in human acute leukemia. Here we present a case of a 7-year-old boy with acute lymphoblastic leukemia (ALL) displaying a tetrasomy 8 clone that could not be detected by conventional cytogenetics. In this study, bone marrow and peripheral blood cells were collected at five different diagnostic stages and analyzed by double targeted fluorescence in situ hybridization (FISH) with centromeric DNA probes for chromosomes 7, 8, 9, and 12. FISH analysis revealed a significant increase in tetrasomy 8 frequency, but not in other chromosomes examined. A smaller increase in trisomy 8 was also detected. At one stage over 60% of the cells were hyperdiploid with 40% being tetrasomic. The size of the tetrasomic clone changed during the course of the disease. The hyperdiploid frequencies of chromosome 8 detected by interphase FISH analysis in bone marrow and peripheral blood were similar. Our findings indicate the utility of FISH analysis in cytogenetic monitoring of leukemia patients and further show that tetrasomy 8 may play a specific role in a subtype of ALL.

Tetrasomy 8 in a patient with acute nonlymphocytic leukemia: a metaphase and interphase study with fluorescence in situ hybridization

Tetrasomy 8 constitutes a relatively rare recurring chromosome defect in myeloid disorders. The patient reported here, a 71-year-old man, presented with tetrasomy 8 as the sole chromosome abnormality associated with an acute nonlymphocytic leukemia of the M2 type. He failed to respond to chemotherapy and died one year after diagnosis. Following conventional cytogenetics and fluorescence in situ hybridization (FISH) with a centromeric probe specific for chromosome 8, tetrasomy 8 was detected in 61% of the metaphases analyzed and trisomy 8 in 39%. FISH analysis of interphase nuclei confirmed the existence of tetrasomic (35%) and trisomic cells (56%) and revealed a number of cells with two chromosomes 8 (8%). This normal population may represent lymphocytes or myeloid cells that escaped conventional analysis due to their inability to divide or to the small number of metaphases available. The relatively higher proportion of tetrasomic cells in metaphase compared with interphase may be attributed to a proliferative advantage of tetrasomic cells in vitro or to the longer duration of their cell cycle. The simultaneous presence of trisomic and tetrasomic cells confirms the hypothesis of a clonal relationship between trisomy 8 and tetrasomy 8. Our case brings further evidence to the specificity of tetrasomy 8 to myeloid disorders and to the association of this chromosome abnormality with a relatively poor prognosis. However, new patients must be studied to further delineate this cytogenetic entity.

A greater incidence of complex translocations in myeloid leukemias than in lymphomas and lymphoid leukemias associated with IGH rearrangement

We have shown that the incidence of complex translocations is approximately the same in chronic myeloid leukemia, characterized by the t(9;22)(q34;q11), and in acute myeloid leukemias, characterized by the t(15;17)(q22;q11) or t(8;21)(q22;q22). This incidence is almost threefold greater than the incidence of complex translocations in lymphomas and lymphoid leukemias characterized by the t(8;14)(q24;q32) or t(14;18)(q32;q21). The genomic recombination, which gives rise to the translocations in lymphoid cells, results mostly from errors of IGH gene rearrangement. Genomic recombination underlying myeloid leukemias has a different cause, and a clue to this may lie in the greater incidence of complex chromosome rearrangements.

Tetrasomy 8 as a clonal anomaly in myeloid neoplasias

Tetrasomy of chromosome 8 as a sole anomaly is apparently extremely rare in acute non-lymphocytic leukemia (ANLL): Only two cases have been reported, one of ANLL (M5b) with this karyotype. Very recently, another case was reported of a myelodysplastic syndrome (MDS) with isolated tetrasomy 8. We report tetrasomy 8 in four cases of ANLL, two of them with M5 and one with M1 subtype. Although in the latter case, tetrasomy 8 was evident in all karyotypes analyzed, in all other cases it constituted a subpopulation of cells other than those with trisomy 8 and those with a normal karyotype (in only one case another change was evident in the karyotype). Using fluorescence in situ hybridization (FISH), the proportion of tetrasomic cells was determined in interphase nuclei. By this technique, small cell populations (3-9%) were detected in three additional trisomy cases. An additional "control" group of five trisomy cases did not show a significant population of tetrasomic interphase nuclei. The data show that tetrasomy 8, if present as a sole anomaly in ANLL, may play a rather specific role for the subtype, and probably for the progression of myeloid neoplasia as well.

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

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

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

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

Frequency of constitutional chromosome alterations in patients with hematologic neoplasias

From 1978 to 1985 cytogenetic studies were performed on 718 patients with different hematologic diseases. Nine (1.25%) had a constitutional chromosome alteration. One patient had trisomy 21, four had balanced translocations and four had sex chromosome anomalies. Although the frequency of constitutional alterations was twice that seen in the newborn population, an analysis of these data and also from the literature shows a random association between constitutional chromosome alterations and hematologic neoplasias, except for patients with Down's syndrome.

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.

Two apparent Philadelphia chromosomes arising from translocations with different chromosomes in a patient with CML: 46,XY,t(7;22)(p22;q11),t(9;22)(q34;q11)

Chromosome studies on bone marrow cells and unstimulated peripheral lymphocytes from a patient with chronic myelogenous leukemia revealed the presence in all cells of two apparent Philadelphia chromosomes: one resulting from the classical translocation with a chromosome #9, and the other arising from a translocation between chromosomes #22 and #7. There was no normal chromosome #22. Some of the cells also had an i(17q), indicative of blast crisis. Repeated chromosome studies at different times during the course of the disease revealed the evolution of additional karyotypic changes. All cells from later samples had an extra #8; some of these cells had a third Philadelphia chromosome, whereas, others had a second Y chromosome. Although a few normal cells were seen in PHA-stimulated lymphocyte cultures, indicating that the patient has a normal constitutional karyotype, most of the cells had a karyotype identical to that found in unstimulated cultures. This unusual karyotype, 46,XY,t(7;22)(p22;q11),t(9;22)(q34;q11), represents the first case in which two apparent Philadelphia chromosomes are present in the leukemic cells from a patient in the absence of a normal #22 chromosome.

High resolution banding of chronic myeloid leukemia chromosomes

Bone marrow aspirates from 29 patients with chronic myeloid leukemia were studied using the methotrexate synchronization culture method. Successful cytogenetic preparations exhibiting long and well banded chromosomes were obtained from all of them. The standard t(9;22) was seen in 23 patients, four had variant translocations, and two were Ph-negative. Of the four patients with variant translocations, one had a simple translocation in which the missing segment of chromosome #22 was translocated onto the short arm of chromosome #9. The remaining three patients had complex translocations. The first involved chromosomes #11, #19, and #22, the second involved chromosomes #9, #11, and #22, and the third involved chromosomes #9, #14, and #22. Karyotypic abnormalities in addition to the Ph chromosome were seen in four patients: in three these changes developed during the chronic phase and in one during the blastic phase. Using Q-, R-, and G-banding techniques, we found that the breakpoint on chromosome #22 is just below the centromere, namely in band 22q11.2 and on chromosome #9 in band 9q34.1. The standard translocation, therefore, can be written as t(9;22)(q34.1;q11.2). Furthermore, the breakpoint on 22q appeared to be identical in all cases with standard as well as the variant translocations. Our results show that the methotrexate synchronization method permits consistent high resolution banding of CML chromosomes, and support the concept that there is no difference in the amount of material translocated from 22q in different patients.

Philadelphia chromosome (Ph) positive chronic myelocytic leukemia (CML): frequency of additional findings

This article documents the cytogenetic findings in 79 patients with typical Ph-positive chronic myelocytic leukemia (CML). Direct preparations of bone marrow and/or peripheral blood of 46 males and 33 females were studied with different banding techniques. Seventy patients were studied during chronic phase. Three (4.3%) had unusual or complex translocations: t(6;22)(p21;q11), t(8;12;9;22)(p21;q21;q34;q11), and t(9;11;22)(q34;q13;q11). One (1.4%) had a +Ph, 1 (1.4%) had a +8, 1 (1.4%) had a del(3)(p13,p23), and 4 of 30 males (13.3%) showed loss of Y chromosome. Five of 8 cases studied during blast crisis had additional abnormalities. The +8 occurred in 4 cases, +10 and +19 each in 3 cases, +6, + 9q+, and +13 each in 2 cases, and +5, +11, +14, +21, +Ph, i(17q), dic(1;9), and structural abnormalities of chromosomes #1, #5, #12, and #13 each in 1 case. Two cases studied in blast crisis alone had complex translocations leading to the Ph. Because it cannot be ruled out that these translocations are secondary, they were not included in the calculation of the frequency of atypical translocations.

Is the chromosomal region 9q34 always involved in variants of the Ph1 translocation?

Six variants of the Ph1 translocation are described. The clinical diagnoses were chronic myeloid leukemia (CML) in 5 cases (patients 1-5) and acute lymphocytic leukemia (ALL) in patient 6. Three Ph1 variants were clear complex translocations, involving chromosomes #9, #22, and a third chromosome, i.e., #16, #11, or #14. The other three Ph1 variants appeared as "simple" translocations between chromosome #22 and chromosome #19, #4, or #12 when G- or Q-banding were used. When studied with high resolution R-banding, a small deletion of the terminal part of one chromosome #9 was visible, strongly suggesting that these variants were also complex translocations, i.e., t(9;19;22)(q34;p13;q11),t(4;9;22) (p16;q34;q11), and t(9;12;22)(q34;p13;q11). In the latter two cases, using in situ hybridization techniques, we demonstrated the presence of c-abl sequences on the Ph1 chromosome. This proved the involvement of 9q34 in these two variants. Our proposal is that most, and probably all, variants of Ph1 are complex translocations involving part of 9q34 and that the conjunction of a specific region of 22q11 with a specific segment of 9q34 (carrying the c-abl protooncogene) is essential for the development of Ph1 + CML.