New chromosome abnormalities and lack of BCL-6 gene rearrangements in Argentinean diffuse large B-cell lymphomas

OBJECTIVES: Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphomas. Cytogenetic studies have revealed a broad spectrum of clonal genetic abnormalities and complex karyotypes. The purpose of this study was to contribute to the understanding of the genomic alterations associated with this group of lymphomas. METHODS: Cytogenetic, fluorescence in situ hybridization (FISH) and molecular analyses were performed in 30 cases with DLBCL: 20 de novo DLBCL (dn-DLBCL) and 10 DLBCL secondary to follicular lymphoma (S-DLBCL). RESULTS: A total of 37 different structural chromosomal rearrangements were found: 27% translocations, 54% deletions, and 19% other alterations. Chromosomes 8, 6, 2, and 9 were the most commonly affected. Interestingly, translocation t(3;14)(q27;q32) and/or BCL-6 gene rearrangements were not observed either by cytogenetic studies or by FISH analysis. Fifteen novel cytogenetic alterations were detected, among them translocations t(2;21)(p11;q22) and t(8;18)(q24;p11.3) appeared as sole structural abnormalities. Translocation t(14;18)(q32;q21) and/or BCL-2-IGH gene rearrangements were the genomic alterations most frequently observed: 50% of S-DLBCL and 30% of dn-DLBCL. Deletions del(4)(q21), del(6)(q27), del(8)(q11), and del(9)(q11) were recurrent. The most common gains involved chromosome regions at 12q13-q24, 7q10-q32, and 17q22-qter; 6q was the most frequently deleted region, followed by losses at 2q35-qter, 7q32-qter, and 9q13-qter. Four novel regions of loss were identified: 5q13-q21, 2q35-qter (both recurrent in our series), 4p11-p12, and 17q11-q12. CONCLUSIONS: These studies emphasize the value of combining conventional cytogenetics with FISH and molecular studies to allow a more accurate definition of the genomic aberrations involved in DLBCL.     

A new recurrent translocation, t(5;11)(q35;p15.5), associated with del(5q) in childhood acute myeloid leukemia. The UK Cancer Cytogenetics Group (UKCCG)

Partial deletion of the long arm of chromosome 5, del(5q), is the cytogenetic hallmark of the 5q-syndrome, a distinct subtype of myelodysplastic syndrome-refractory anemia (MDS-RA). Deletions of 5q also occur in the full spectrum of other de novo and therapy-related MDS and acute myeloid leukemia (AML) types, most often in association with other chromosome abnormalities. However, the loss of genetic material from 5q is believed to be of primary importance in the pathogenesis of all del(5q) disorders. In the present study, we performed fluorescence in situ hybridization (FISH) studies using a chromosome 5-specific whole chromosome painting probe and a 5q subtelomeric probe to determine the incidence of cryptic translocations. We studied archival fixed chromosome suspensions from 36 patients with myeloid disorders (predominantly MDS and AML) and del(5q) as the sole abnormality. In 3 AML patients studied, this identified a translocation of 5q subtelomeric sequences from the del(5q) to the short arm of an apparently normal chromosome 11. FISH with chromosome 11-specific subtelomeric probes confirmed the presence of 11p on the shortened 5q. Further FISH mapping confirmed that the 5q and 11p translocation breakpoints were the same in all 3 cases, between the nucleophosmin (NPM1) and fms-related tyrosine kinase 4 (FLT4) genes on 5q35 and the Harvey ras-1-related gene complex (HRC) and the radixin pseudogene (RDPX1) on 11p15.5. Importantly, all 3 patients with the cryptic t(5;11) were children: a total of 3 of 4 AML children studied. Two were classified as AML-M2 and the third was classified as M4. All 3 responded poorly to treatment and had short survival times, ranging from 10 to 18 months. Although del(5q) is rare in childhood AML, this study indicates that, within this subgroup, the incidence of cryptic t(5;11) may be high. It is significant that none of the 24 MDS patients studied, including 11 confirmed as having 5q-syndrome, had the translocation. Therefore, this appears to be a new nonrandom chromosomal translocation, specifically associated with childhood AML with a differentiated blast cell phenotype and the presence of a del(5q).     

Cytogenetic and molecular diagnosis of chromosome 5 deletions in myelodysplasia

Deletions of chromosome 5, del(5q), are frequently observed in myelodysplasia (MDS). We evaluated molecular detection of loss of heterozygosity (LOH) as a diagnostic method to detect del(5q) in a series of 60 MDS cases at a single institution. LOH was compared to cytogenetics on the same clinical specimen, resolving ambiguous cases by fluorescent in situ hybridization (FISH) and additional LOH. There was poor concordance between molecular and cytogenetic results, but most discrepancies could be resolved by FISH and additional LOH. Molecular analysis was of low sensitivity because most cases contained a relatively high proportion of cells without del(5q), but it was accurate, while cytogenetics overestimated the proportion of cells with del(5q) and failed to detect some cases with complex rearrangements. Minor clones were detected both by FISH and LOH. Overall, we found an incidence of 23% (14 of 60 cases) for del(5q) in MDS. The results also suggest that there is a high degree of genetic heterogeneity in the cellular population of MDS. Although del(5q) is common in MDS, it may not be present in all cells, leading to diagnostic challenges.     

Absence of MLL gene rearrangement in de novo myelodysplastic syndromes (MDS)

The Mixed Lineage Leukemia (MLL) gene has been identified in 11q23 translocations. The aim of the present study is the investigation of the frequency of MLL gene rearrangements in cases of de novo myelodysplastic syndromes (MDS). Sixty-two patients with de novo MDS were included in the analysis. The detection of MLL gene rearrangements was performed by Southern blot. Clonal karyotypic abnormalities were found in 15/50 (30%) cases. 11q23 abnormalities were not detected. One case with RAEB and a complex karyotype presented a del (11)(q13); further analysis by FISH revealed loss of one copy of MLL gene in all metaphases. Southern blot revealed germline bands in all cases using Eco RI and in 61/62 cases with Bam HI. The case with RAEB and a del (11)(q13) revealed a rearranged band following only Bam HI digestion, but not Eco RI. Rearrangements of MLL gene within exons 5–9 were not identified in this series of adult de novo MDS, indicating that this molecular abnormality is not involved in the pathogenesis of this group of hemopoietic disorders.     

Genetics of small lymphocyte disorders.

Cytogenetic analysis of small lymphocytes disorders is hindered by the low mitotic activity of the malignant cells. The use of fluorescence in situ hybridization (FISH) allows the detection of chromosomal amplifications, deletions, or translocations at a single-cell level in dividing and resting cells. The use of FISH in combination with other molecular techniques has defined the deletion in band 13q14 as the most common abnormality in chronic lymphocytic leukemia, followed by del (11)(q22-23), trisomy 12, del (17)(p13), and del (6)(q21). The del 13q14 is also found in 70% of mantle-cell lymphomas (MCLs) and in non-Hodgkin's lymphoma (NHL), acute lymphoblastic leukemia (ALL), and multiple myeloma (MM) patients. These findings point to the existence of yet unidentified tumor-suppressor gene(s) at the 13q14 locus, the loss/inactivation of which leads to B-cell neoplasia. Del (17(p13) (involving the p53 tumor-suppressor gene) and del (11)(q22-23) (involving the ataxia-telangiectasia gene [ATM]) seem to be independent prognostic factors for poor survival in chronic lymphocytic leukemia (CLL) patients. In MCL, the t(11;14) involving the bcl-1 gene is found, but data from a bcl-1 transgenic animal model suggest that hyperexpression of bcl-1 is not sufficient for lymphomatogenesis. Similar data are observed in bcl-2 transgenic animals, a finding showing that the bcl-2 hyperexpression observed in t(14;18)-positive follicular lymphoma cells is not sufficient to confer a malignant phenotype. The contribution of other chromosomal abnormalities other than bcl-1 and bcl-2 rearrangements in the pathogenesis of MCL and follicular-cell lymphomas has to be determined.     

Acute lymphoblastic leukaemia: diagnosis and classification

Acute lymphoblastic leukaemia (ALL) is a heterogeneous disease with distinct biological and prognostic groupings. Diagnosis relies on traditional cytomorphological and immunohistochemical evaluation of the leukaemic blasts. Subsequently, cytogenetic analysis identifies clonal numeric and/or structural chromosomal abnormalities that may be present, thus confirming the subtype classification and providing important prognostic information for treatment planning. The major chromosomal abnormalities in ALL are t(9;22)(q34;q11), t(12;21)(p13;q22), t(4;11)(q21;q23), t(1;19)(q23;p13), 8q24 translocations and hyperdiploidy. Generally, hyperdiploidy, occurring most frequently in paediatric cases, is associated with a good prognosis, while hypodiploidy confers a poor prognosis. Among structural chromosomal abnormalities, the t(9;22)(q34;q11) resulting in the BCR/ABL fusion protein, and rearrangements of the MLL gene, confer a poor prognosis in both children and adults, while t(12;21)(p13;q22), resulting in the TEL/AML1 fusion protein, and del (12p) confer a good prognosis. More recently, additional diagnostic and prognostic information has been gained from fluorescence in situ hybridization (FISH) and DNA microarray techniques.     

Azacitidine treatment for patients with myelodysplastic syndrome and acute myeloid leukemia with chromosome 3q abnormalities

Acute Myeloid Leukemia (AML) and myelodysplasia (MDS) with chromosome 3q abnormalities have a dismal outcome either untreated or with conventional treatments. Azacitidine (AZA) is now considered as the standard of care in high‐risk MDS and oligoblastic AML patients. The objective of this study was to evaluate the impact of azacitine treatment in this cytogenetic subgroup. We report here a multicentre retrospective study of 157 patients treated with AZA for AML/MDS with chromosome 3q abnormalities and 27 patients with isolated EVI‐1 overexpression. Median age was 65 years, 40 patients (25%) had inv(3)(q21q26.2) or t(3;3)(q21;q26.2), 36 patients (23%) had other balanced 3q26 rearrangements, 8 patients (5%) had balanced 3q21 rearrangements and 73 patients (46%) had other 3q abnormalities. The overall response rate was 50% (29% CR). Median overall survival was 10.6 months. By multivariate analysis, patients with lower bone marrow blast counts, higher platelet counts, non‐complex cytogenetics, and absence of prior treatment with intensive chemotherapy had a better outcome. 27 patients were allo‐transplanted and achieved a 21‐month median OS. Balanced 3q21 translocations were associated with a better response rate and overall survival. Outcome of patients with isolated EVI‐1 overexpression was comparable to that of patients with chromosome 3q lesions. Thus, AML/MDS patients with 3q abnormalities appear to be a heterogeneous group in their response to AZA, and AZA may represent a suitable option in particular as a bridge to allogeneic transplantation. Am. J. Hematol. 90:859–863, 2015. © 2015 Wiley Periodicals, Inc.     

Molecular characterization of 12p abnormalities in hematologic malignancies: deletion of KIP1, rearrangement of TEL, and amplification of CCND2

Twenty patients with hematologic malignancies with 12p abnormalities were investigated by fluorescence in situ hybridization (FISH) using probes mapped to specific regions in 12p. The initial analysis using the YAC 964c10 (D12S736) revealed that all four cases with cytogenetically identified del(12p) had lost one copy of this YAC and that submicroscopic deletions had occurred in 10 of the 16 neoplasms with other 12p abnormalities, ie, translocations, additions, and insertions. The deletions were partially mapped with cosmids localized to subregions of 12p. One copy of the gene for p27kip1 (KIP1), involved in cell cycle entrance, was found to be lost in all cases in which deletions could be detected by other probes and in one case with a translocation as the only detectable change. This implicates KIP1 as a possible tumor suppressor gene affected by del(12p). Four translocations with no apparent concomitant deletions were detected. All four breakpoints resulted in a split D12S736 signal. In two of these cases, we showed that TEL was disrupted as a result of a t(5;12)(q32-33;p12) and a t(12;22)(p12;q12), respectively. Two lymphoid neoplasm--one non-Hodgkin's lymphoma and one Burkitt's lymphoma--with 12p amplifications were detected. In both cases cyclin D2 (CCND2) was within the amplified region. Thus, cytogenetic abnormalities of 12p in hematologic malignancies result in at least three different molecular changes: deletions of KIP1, amplifications of CCND2, and structural rearrangements of TEL.     

Trisomy 3 in marginal zone B-cell lymphoma: a study based on cytogenetic analysis and fluorescence in situ hybridization

Trisomy 3 represents the most frequent and consistent chromosomal abnormality characterizing the recently defined entity marginal zone B-cell lymphoma (MZBCL). By cytogenetic analysis and/or fluorescence in situ hybridization (FISH) on interphase nuclei we found an increased copy number of chromosome 3 in 22/36 (61%) successfully analysed cases, including 8/12 cases with extranodal MZBCL, 8/13 cases with nodal MZBCL, and 6/11 patients with splenic MZBCL. Sensitivity of interphase cytogenetics was somewhat higher than that of conventional cytogenetic investigation. Structural chromosomal changes involving at least one chromosome 3 were seen in 11/20 cases with an increased copy number of chromosome 3: +del(3)(p13) was demonstrated in three cases, and was the sole chromosomal abnormality in one of them; +i(3)(q10) was seen in two other patients; and rearrangements involving various breakpoints on the long arm of chromosome 3 were found in the remaining cases. FISH on metaphase spreads confirmed these structural abnormalities and additionally showed two unexpected translocations involving chromosome 3. We conclude that: (1) trisomy 3 occurs in a high proportion of extranodal, nodal and splenic MZBCL; (2) FISH on interphase nuclei is an additional and sensitive tool in detecting an increased copy number of chromosome 3 in MZBCL; (3) additional structural abnormalities involving the long arm of chromosome 3 are frequent but non-recurrent and are perhaps secondary changes; and (4) abnormalities such as +del(3)(p13) and +i(3)(q10) suggest that genes located on the long arm of chromosome 3 are of particular importance in the pathogenesis of MZBCL.     

Cytogenetic and FISH studies of a single center consecutive series of 152 childhood acute lymphoblastic leukemias

Between 1977 and 1996, cytogenetic investigations were performed on 182 childhood (< or = 16 yr) acute lymphoblastic leukemias (ALL), constituting 94% (182 of 194) of all ALL patients diagnosed and treated at the Departments of Pediatrics, Lund and Malmo University Hospitals, Sweden, during these two decades. The cytogenetic analyses were successful in 152 cases (84%). The failure rate was higher for the ALL investigated before 1987 (30% vs. 4%, p < 0.0001), and also the incidence of cytogenetically normal cases was higher during 1977-86 (43% vs. 25%, p < 0.05). Clonal chromosomal abnormalities were found in 103 (68%) ALL. Structural rearrangements were detected, by chromosome banding alone, in 76 cases (50%). Fluorescence in situ hybridization (FISH) was used to identify cases with t(12;21), 11q23 rearrangements, and 9p deletions, using probes for ETV6/CBFA2, MLL, and CDKN2A/B, in 72 cases from which cells in fixative and/or unstained metaphase preparations were available. In total, the most common structural rearrangements were del(9p) (17%), t(12;21) (15%), del(6q) (8%), and MLL rearrangements (4%). Six (32%) of nineteen cytogenetically normal ALL analyzed by FISH harbored cryptic abnormalities; three displayed t(12;21) and four had del(9p), one of which also carried a t(12;21). Five (45%) of the t(12;21)-positive ALL showed +der(21)t(12;21) or ider(21)(q10)t(12;21), resulting in the formation of double fusion genes. Among the more rare aberrations, eight structural rearrangements were identified as novel recurrent ALL-associated abnormalities, and nine cases harbored rearrangements previously not reported. Sixteen cases displayed karyotypically unrelated clones at different investigations. Seven ALL (5%) showed simple chromosomal changes, unrelated to the aberrations detected at diagnosis, during morphologic and clinical remission, and in all but one instance the patients remained in remission, with the abnormal clone disappearing in subsequent investigations. This indicates that the emergence of novel clonal chromosomal aberrations during remission in childhood ALL is rather common and does not by necessity predict a forthcoming relapse.     

Different genetic pathways in leukemogenesis for patients presenting with therapy-related myelodysplasia and therapy-related acute myeloid leukemia

Development of myelodysplasia (MDS) with subsequent progression to acute myeloid leukemia (AML) is an example of the multistep process of malignant transformation in which each step often relates to genetic abnormalities that can be directly seen as chromosomal aberrations. Therapy-related MDS and AML (t-MDS and t-AML) may serve as an ideal model for a study of the genetic evolution of MDS and AML because chromosomal abnormalities are observed in most cases and because the disease is often diagnosed early due to a close patient follow-up. The cytogenetic characteristics at diagnosis were studied in 137 consecutive cases of t-MDS and t-AML, including 22 new cases, and correlated with the clinical characteristics and the course of the disease. Balanced translocations to chromosome bands 11q23 and 21q22 represent primary steps in pathways leading directly to overt t-AML. Specific chromosomal deletions or losses, on the other hand, represent primary or secondary events in alternative pathways leading to t-MDS with potential for subsequent transformation to overt t-AML. Loss of a whole chromosome 7 (-7) or deletion of its long arm (7q-) and deletion of the long arm of a chromosome 5 (5q-) were the most frequent primary abnormalities significantly related to t-MDS. Loss of a whole chromosome 5 (-5) was also a primary event, but surprisingly, was observed equally in t-MDS and in t-AML. Deletion of chromosome 13, including bands q13q14, was another less common primary aberration of t- MDS. Except for -7 and del(13q), these primary aberrations were most often observed together with secondary abnormalities. These included balanced aberrations involving band 3q26 and various deletions of chromosome 3, a gain of a whole chromosome 8, deletions of the short arm or loss of chromosomes 12 and 17, loss of a whole chromosome 18, and deletions of the short arm of chromosome 21. Deletions or loss or chromosomes 5 and 7 were significantly associated with previous therapy with alkylating agents (P = .002), and balanced translocations to chromosome bands 3q26, 11q23, and 21q22 were significantly associated with previous therapy with drugs targeting DNA-topoisomerase II (P < .00005). Other characteristic aberrations were not related to any specific type of therapy. The molecular changes believed to contribute to the development of t-MDS and t-AML have been identified for many of these chromosomal abnormalities.     

Chromosome aberrations in a series of 120 multiple myeloma cases with abnormal karyotypes

We identified 120 multiple myeloma (MM) cases with satisfactory cytogenetic evaluation and abnormal karyotypes. Hyperdiploid karyotype was found in 77 cases (64%), hypodiploid in 30 cases (25%), and the remaining 13 cases (11%) had a pseudodiploid karyotype. The most common numerical abnormalities were gains of chromosomes 15, 9, 3 followed by chromosomes 19, 11, 7, 21, and 5. Whole chromosome losses were also frequent involving primarily chromosomes X/Y, 8, 13, 14, and 22. Most cases showed also structural rearrangements leading to del(1p), dup(1q), del(5q), del(6q), del(8p), del(9p), del(13q), and del(17p). Chromosome 13/13q deletion was found in 52% of cases; complete loss of 13 was observed in 73% of cases, whereas 27% had interstitial deletions. In addition, 13/13q deletions occurred in 75% of nonhyperdiploid myeloma but only 39% of the hyperdiploid had 13/13q deletions. Translocations affecting 14q32/IGH region was seen 40 cases; t(11;14)(q13;q32) in 17 cases, t(14;16)(q32;q23) and t(8;14)(q24;q32) in three cases each, and t(6;14)(p21;q32) and t(1;14)(q21;q32) in two cases each. The remaining 14q32 translocations had various t(V;14) partners or of an undetermined origin. Remarkably, the 14q32/IGH translocations were less frequent in the hyperdiploid karyotypes than the nonhyperdiploid karyotypes (17 vs. 63%). Fourteen cases showed break at 8q24/CMYC site; seven of those had Burkitt's-type translocations. Our results revealed that conventional cytogenetics remains an important tool in elucidating the complex and divers genetic anomalies of MM. Cytogenetics identifies two distinct groups of MM, hyperdiploid and nonhyperdiploid, and establishes the presence of prognostic chromosomal markers such as 13/13q, 17p, 8q24, and 16q aberrations.     

Waldenström macroglobulinemia neoplastic cells lack immunoglobulin heavy chain locus translocations but have frequent 6q deletions

Lymphoplasmacytic lymphoma (LPL) is characterized by t(9;14)(p13;q32) in 50% of patients who lack paraproteinemia. Waldenstr?m macroglobulinemia (WM), which has an immunoglobulin M (IgM) paraproteinemia, is classified as an LPL. Rare reports have suggested that WM sometimes is associated with 14q23 translocations, deletions of 6q, and t(11;18)(q21;q21). We tested for these abnormalities in the clonal cells of WM patients. We selected patients with clinicopathologic diagnosis of WM (all had IgM levels greater than 1.5 g/dL). Southern blot assay was used to detect legitimate and illegitimate IgH switch rearrangements. In addition to conventional cytogenetic (CC) and multicolor metaphase fluorescence in situ hybridization (M-FISH) analyses, we used interphase FISH to screen for t(9;14)(p13;q32) and other IgH translocations, t(11;18)(q21;q21), and 6q21 deletions. Genomic stability was also assessed using chromosome enumeration probes for chromosomes 7, 9, 11, 12, 15, and 17 in 15 patients. There was no evidence of either legitimate or illegitimate IgH rearrangements by Southern blot assay (n = 12). CC (n = 37), M-FISH (n = 5), and interphase FISH (n = 42) failed to identify IgH or t(11;18) translocations. Although tumor cells from most patients were diploid for the chromosomes studied, deletions of 6q21 were observed in 42% of patients. In contrast to LPL tumors that are not associated with paraproteinemia and that have frequent t(9;14)(p13;q32) translocations, IgH translocations are not found in WM, a form of LPL tumor distinguished by IgM paraproteinemia. However, WM tumor cells, which appear to be diploid or near diploid, often have deletions of 6q21.     

Novel translocations that disrupt the platelet-derived growth factor receptor beta (PDGFRB) gene in BCR-ABL-negative chronic myeloproliferative disorders

The BCR-ABL-negative chronic myeloproliferative disorders (CMPD) and myelodysplastic/myeloproliferative diseases (MDS/MPD) are a spectrum of related conditions for which the molecular pathogenesis is poorly understood. Translocations that disrupt and constitutively activate the platelet-derived growth factor receptor beta(PDGFRB) gene at chromosome band 5q33 have been described in some patients, the most common being the t(5;12)(q33;p13). An accurate molecular diagnosis of PDGFRB-rearranged patients has become increasingly important since recent data have indicated that they respond very well to imatinib mesylate therapy. In this study, we have tested nine patients with a CMPD or MDS/MPD and a translocation involving 5q31-33 for disruption of PDGFRB by two-colour fluorescence in situ hybridization (FISH) using differentially labelled, closely flanking probes. Normal control interphase cells gave a false positive rate of 3% (signals more than one signal width apart). Six patients showed a pattern of one fused signal (from the normal allele) and one pair of signals separated by more than one signal width in > 85% of interphase cells, indicating that PDGFRB was disrupted. These individuals had a t(1;5)(q21;q33), t(1;5)(q22;q31), t(1;3;5)(p36;p21;q33), t(2;12;5)(q37;q22;q33), t(3;5) (p21;q31) and t(5;14)(q33;q24) respectively. The remaining three patients with a t(1;5)(q21;q31), t(2;5)(p21;q33) and t(5;6)(q33;q24-25) showed a normal pattern of hybridization, with > or = 97% interphase cells with two fusion signals. We conclude that two-colour FISH is useful to determine the presence of a PDGFRB rearrangement, although, as we have shown previously, this technique may not detect subtle complex translocations at this locus. Our data indicate that several PDGFRB partner genes remain to be characterized.     

Cytogenetic analysis in patients with primary myelodysplastic syndromes in leukaemic transformation: A report on 94 cases

A series of 94 patients presenting primary refractory anaemia with excess of blasts in transformation or acute myeloid leukaemia occurring after a myelodysplastic stage was submitted to retrospective cytogenetic analysis by the Groupe Français de Cytogénétique Hématologique. The aim of this collaborative study was to analyze the patterns of chromosome abnormalities appearing in primary myelodysplastic syndromes (MDS) in leukaemic transformation. As previously described in the literature, the most common chromosome aberrations involved del(5q), -7, +8, 17, 11, 12p and del(20q), while abnormalities of chromosome 17p were more frequently detected during the leukaemic transformation of MDS. The translocations t(2;3)(p22–23;q26–28) and whole arm t(17;18) were confirmed to be nonrandom events in these myeloid disorders.     

Abnormalities of the long arm of chromosome 6 in childhood acute lymphoblastic leukemia

To determine the biologic significance of the structural rearrangements of the long arm of chromosome 6(6q) in acute lymphoblastic leukemia (ALL) at diagnosis, we studied 412 consecutive children whose leukemic cell chromosomes had been completely banded and identified 45 (11%) children with this abnormality. The 45 cases were divided into del(6q) only (n = 11), del(6q) and numerical abnormalities (n = 4), del(6q) and structural abnormalities (n = 23), and 6q translocations (n = 7). The breakpoints of del(6q) were subgrouped: del(6)(q15q21) in 11 cases, del(6) (q13q21) in six, del(6)(q21q23) in four, del(6)(q15) in four, del(6)(q15q23) in three, and other deletions in 10 cases. Notably, all these deletions encompassed the 6q21 band, suggesting that this might be the locus of a recessive tumor suppressor gene, the absence of which contributes to malignant transformation or proliferation. Among the seven children with 6q translocations, a previously unidentified nonrandom translocation, t(6;12)(q21;p13) was noted in two cases with an early pre-B immunophenotype. Clinical features and event-free survival were similar among children with or without 6q abnormalities. Overall, children with 6q abnormalities were less likely than those without the abnormality to have a pre-B immunophenotype (P = .03). T-cell immunophenotypes were equally represented in cases with or without 6q abnormalities. However, all four children with del(6q) and a 12p abnormality had early pre-B ALL and all three children with del(6q) and a 9p abnormality had a T-cell immunophenotype. The lack of specificity for a particular immunophenotype may imply that the gene or genes affected by 6q abnormalities are broadly active in the multistep process of lymphoid leukemogenesis. The relatively high frequency of microscopically visible del(6q) indicates the need for molecular studies to identify cases with submicroscopic deletions.     

Exploring polycythaemia vera with fluorescence in situ hybridization: additional cryptic 9p is the most frequent abnormality detected

Between 1986 and 2001, 220 patients with polycythaemia vera (PV) were studied using conventional cytogenetics. Of 204 evaluable patients, 52 (25.4%) had clonal abnormalities. The recurrent chromosomal rearrangements were those of chromosome 9 (21.1%), del(20q) (19.2%), trisomy 8 (19.2%), rearrangements of 13q (13.4%), abnormalities of 1q (11.5%), and of chromosomes 5 and 7 (9.6%). Subsequent analysis of 32 patients, performed at follow-up of up to 14.8 years, revealed new clonal abnormalities in five patients and the disappearance of an abnormal clone in four. Eleven patients remained normal up to 11.5 years and seven patients maintained an abnormality for over 10 years. Fifty-three patients were studied retrospectively using interphase fluorescence in situ hybridization (I-FISH), utilizing probes for centromere enumeration of chromosomes 8 and 9, and for 13q14 and 20q12 loci. Conventional cytogenetics demonstrated clonal chromosome abnormalities in 23% of these 53 patients. The addition of I-FISH increased the detection of abnormalities to 29% and permitted clarification of chromosome 9 rearrangements in an additional 5.6% of patients. FISH uncovered rearrangements of chromosome 9 in 53% of patients with an abnormal FISH pattern, which represented the most frequent genomic alteration in this series.     

Translocations and deletions of 5q13.1 in myelodysplasia and acute myelogenous leukemia: evidence for a novel critical locus

Acquired partial and complete deletions of chromosome 5 (5q-, -5) are common cytogenetic anomalies associated with myelodysplasia (MDS) and acute myeloid leukemia (AML). A critical region of consistent loss at 5q31.1 (in > 90% of cases) has led us and others to postulate the presence of a key negative regulator(s) of leukemogenesis. Although the interstitial deletion limits vary among patients, del(5) (q13q33) and del(5)(q13q35) constitute major subsets. Furthermore, it is not rare to encounter deletions, translocations, or paracentric inversions involving 5q11 to 5q13, which indicates inactivation or disruption of important gene(s) at that locus. In this report, we have localized a novel locus at 5q13.1 to a 2.0-Mb interval between the anonymous markers D5S672 and GATA-P1804. This locus resided within the region of loss in 12 of 27 patients with anomalies of chromosome 5; one of these cases had apparent retention of both alleles of all the telomeric loci. Fluorescence in situ hybridization (FISH) studies demonstrate that the AML cell line ML3 is disrupted at 5q13.1 by a translocation involving chromosome 3, with apparent retention of the entire chromosome 5 sequence. Our results suggest that this novel proximal locus encodes a critical gene that may be deleted or disrupted in a subset of MDS/AML patients with chromosome 5 anomalies.