Genetic differences between paediatric and adult Burkitt lymphomas.

Dysregulation of MYC is the genetic hallmark of Burkitt lymphoma (BL) but it is encountered in other aggressive mature B-cell lymphomas. MYC dysregulation needs other cooperating events for BL development. We aimed to characterize these events and assess the differences between adult and paediatric BLs that may explain the different outcomes in these two populations. We analysed patterns of genetic aberrations in a series of 24 BLs: 11 adults and 13 children. We looked for genomic imbalances (copy number variations), copy-neutral loss of heterozygosity (CN-LOH) and mutations in TP53, CDKN2A, ID3 (exon 1), TCF3 (exon17) and CCND3 (exon 6). Young patients displayed more frequent 13q31.3q32.1 amplification, 7q32q36 gain and 5q23.3 CN-LOH, while 17p13 and 18q21.3 CN-LOH were only detected in adult BLs. ID3 mutations were present in all adult samples, but only in 42% of childhood cases. CCND3 and ID3 double-hit mutations, as well as 18q21 CN-LOH, seemed to be associated with poorer outcome. For the first time, we report different genetic anomalies between adult and paediatric BLs, suggesting age-related heterogeneity in Burkitt lymphomagenesis. This may explain the poorer prognosis of adult BLs. Additional studies are needed to confirm these results in the setting of clinical trials.

Different outcome of T cell acute lymphoblastic leukemia with translocation t(11;14) treated in two consecutive children leukemia group EORTC trials.

Acute lymphoblastic leukemia of T cell lineage (T-ALL) is an aggressive malignant disease which accounts for 15 % of childhood ALL. T(11;14) is the more frequent chromosomal abnormality in childhood T-ALL, but its prognostic value remained controversial. Our aim was to analyze the outcome of childhood T-ALL with t(11;14) to know if the presence of this translocation is associated with a poor prognosis. We conducted a retrospective study from a series of 20 patients with t(11;14), treated in two consecutive trials from the European Organization for Research and Treatment of Cancer Children Leukemia Group over a 19-year period from 1989 to 2008. There were no significant differences between the 2 consecutive groups of patients with t(11;14) regarding the clinical and biological features at diagnosis. Among 19 patients who reached complete remission, 9 patients relapsed. We noticed 7 deaths all relapse- or failure-related. In the 58881 study, a presence of t(11;14) was associated with a poor outcome with an event-free survival at 5 years at 22.2 % versus 65.1 % for the non-t(11;14) T-ALL (p = 0.0004). In the more recent protocol, the outcome of T-ALL with t(11;14) reached that of non-t(11;14) T-ALL with an event-free survival at 5 years at 65.5 versus 74.9 % (p = 0.93). The presence of t(11;14) appeared as a poor prognostic feature in the 58881 trial whereas this abnormality no longer affected the outcome in the 58951 study. This difference is probably explained by the more intensive chemotherapy in the latest trial.

Dexamethasone (6 mg/m2/day) and prednisolone (60 mg/m2/day) were equally effective as induction therapy for childhood acute lymphoblastic leukemia in the EORTC CLG 58951 randomized trial.

Dexamethasone could be more effective than prednisolone at similar anti-inflammatory doses in the treatment of childhood acute lymphoblastic leukemia. In order to check if this "superiority" of dexamethasone might be dose-dependent, we conducted a randomized phase III trial comparing dexamethasone (6 mg/m(2)/day) to prednisolone (60 mg/m(2)/day) in induction therapy. All newly diagnosed children and adolescents with acute lymphoblastic leukemia in the 58951 EORTC trial were randomized on prephase day 1 or day 8. The main endpoint was event-free survival; secondary endpoints were overall survival and toxicity. A total of 1947 patients with acute lymphoblastic leukemia were randomized. At a median follow-up of 6.9 years, the 8-year event-free survival rate was 81.5% in the dexamethasone arm and 81.2% in the prednisolone arm; the 8-year overall survival rates were 87.2% and 89.0% respectively. The 8-year incidences of isolated or combined central nervous system relapse were 2.9% and 4.5% in the dexamethasone and prednisolone arms, respectively. The incidence of grade 3-4 toxicities during induction and the frequency of osteonecrosis were similar in the two arms. In conclusion, dexamethasone and prednisolone, used respectively at the doses of 6 and 60 mg/m(2)/day during induction, were equally effective and had a similar toxicity profile. Dexamethasone decreased the 8-year central nervous system relapse incidence by 1.6%. This trial was registered at www.clinicaltrials.gov as #NCT00003728.

Constitutional and somatic rearrangement of chromosome 21 in acute lymphoblastic leukaemia.

Changes in gene dosage are a major driver of cancer, known to be caused by a finite, but increasingly well annotated, repertoire of mutational mechanisms. This can potentially generate correlated copy-number alterations across hundreds of linked genes, as exemplified by the 2% of childhood acute lymphoblastic leukaemia (ALL) with recurrent amplification of megabase regions of chromosome 21 (iAMP21). We used genomic, cytogenetic and transcriptional analysis, coupled with novel bioinformatic approaches, to reconstruct the evolution of iAMP21 ALL. Here we show that individuals born with the rare constitutional Robertsonian translocation between chromosomes 15 and 21, rob(15;21)(q10;q10)c, have approximately 2,700-fold increased risk of developing iAMP21 ALL compared to the general population. In such cases, amplification is initiated by a chromothripsis event involving both sister chromatids of the Robertsonian chromosome, a novel mechanism for cancer predisposition. In sporadic iAMP21, breakage-fusion-bridge cycles are typically the initiating event, often followed by chromothripsis. In both sporadic and rob(15;21)c-associated iAMP21, the final stages frequently involve duplications of the entire abnormal chromosome. The end-product is a derivative of chromosome 21 or the rob(15;21)c chromosome with gene dosage optimized for leukaemic potential, showing constrained copy-number levels over multiple linked genes. Thus, dicentric chromosomes may be an important precipitant of chromothripsis, as we show rob(15;21)c to be constitutionally dicentric and breakage-fusion-bridge cycles generate dicentric chromosomes somatically. Furthermore, our data illustrate that several cancer-specific mutational processes, applied sequentially, can coordinate to fashion copy-number profiles over large genomic scales, incrementally refining the fitness benefits of aggregated gene dosage changes.

Chromosomal translocations involving the IGH@ locus in B-cell precursor acute lymphoblastic leukemia: 29 new cases and a review of the literature.

Chromosomal translocations involving the immunoglobulin heavy chain locus (IGH@) are recurrent but rare in B-cell precursor acute lymphoblastic leukemia (BCP-ALL), and various partner genes have been described. Here, we report a new series of 29 cases of BCP-ALL with IGH@ translocations. The partner gene was identified by fluorescence in situ hybridization and/or molecular cloning in 20 patients. Members of the CEBP gene family (n = 11), BCL2 (n = 3), ID4 (n = 3), EPOR (n = 2), and TRA/D@ (n = 1) were identified and demonstrated by quantitative real-time reverse transcriptase-polymerase chain reaction to be markedly up-regulated. The present cases, added to those already reported, confirm the diversity of the partner genes, which, apart from BCL2, are specific to BCP-ALL. Collectively, patients with IGH@ translocations may represent a novel sub-group of BCP-ALL occurring in adolescents and young adults.

Time from diagnosis to intensive chemotherapy initiation does not adversely impact the outcome of patients with acute myeloid leukemia.

In acute myeloid leukemia (AML), new strategies assess the potential benefit of genetically targeted therapy at diagnosis. This implies waiting for laboratory tests and therefore a delay in initiation of chemotherapy. We studied the impact of time from diagnosis to treatment (TDT) on overall survival, early death, and response rate in a retrospective series of 599 newly diagnosed AML patients treated by induction chemotherapy between 2000 and 2009. The effect of TDT was assessed using multivariate analysis. TDT was analyzed as a continuous variable using a specific polynomial function to model the shape and form of the relationship. The median TDT was 8 days (interquartile range, 4-16) and was significantly longer in patients with a white blood cell count (WBC) <50 Giga per liter (G/L) (P < .0001) and in older patients (P = .0004). In multivariate analysis, TDT had no impact on overall survival (P = .4095) compared with age >60 years, secondary AML, WBC >50 G/L, European LeukemiaNet risk groups, and Eastern Cooperative Oncology Group performance status. Furthermore, TDT was not associated with response rate and early death. Thus, waiting a short period of time for laboratory tests to characterize leukemias better and design adapted therapeutic strategies at diagnosis seems possible.

Hyperdiploidy with 58-66 chromosomes in childhood B-acute lymphoblastic leukemia is highly curable: 58951 CLG-EORTC results.

The aim of our study was to analyze the factors contributing to heterogeneity of prognosis in patients with hyperdiploidy>50 chromosomes (HD>50), a group of B-cell precursor acute lymphoblastic leukemia with favorable outcome. The 541 HD>50 patients registered prospectively in the 58951 European Organisation for Research and Treatment of Cancer (EORTC) Children's Leukemia Group (CLG) trial, identified by karyotype (446 patients) and by DNA index (DI) (490 patients), had a 6-year event-free survival (EFS) of 89.0% (standard error [SE] = 1.5%) and a 6-year overall survival (OS) of 95.9% (SE = 0.9%). The strongest prognostic factor was the modal number of chromosomes (MNC): the 6-year EFS of 51-53, 54-57, and 58-66 MNC groups were 80%, 89%, and 99%, respectively (P < .0001). Ploidy assessed by DI was also a favorable factor: the higher the DI, the better the outcome. The 6-year EFS of the 3 subgroups of DI < 1.16/≥1.16-<1.24/≥1.24 were 83%, 90%, and 95%, respectively (P = .009). All usual combinations of trisomies (chromosomes 4, 10, 17, 18) were significant favorable factors but had lower EFS when MNC was lower than 58. In multivariate analysis, MNC remained the strongest factor. Consequently, the best indicator for excellent outcome was ploidy assessed by karyotype because patients with 58-66 chromosomes stood every chance of being cured (OS of 100% at 6-year follow-up) with less-intensive therapy. This trial was registered at www.clinicaltrials.gov as #NCT00003728. Registered: http://www.eortc.org/, http://clinicaltrials.gov/show/NCT00003728.

Patterns of genomic aberrations suggest that Burkitt lymphomas with complex karyotype are distinct from other aggressive B-cell lymphomas with MYC rearrangement.

We previously showed that complex karyotypes (CK) and chromosome 13q abnormalities have an adverse prognostic impact in childhood Burkitt lymphomas/leukemias (BL) and diffuse large B-cell lymphomas (DLBCL). The aim of our study was to identify recurrent alterations associated with MYC rearrangements in aggressive B-cell lymphomas with CK. Multicolor fluorescence in situ hybridization (M-FISH) was performed in 84 patient samples (59 adults and 25 children), including 37 BL (13 lymphomas and 24 acute leukemias), 12 DLBCL, 28 B-cell lymphomas with intermediate features (DLBCL/BL), 4 B-cell precursor acute lymphoblastic leukemias (BCP-ALL), and 3 unclassifiable B-cell lymphomas. New (cytogenetically undetected) abnormalities were identified in 80% of patients. We also refined one-third of the chromosomal aberrations detected by karyotyping. M-FISH proved to be more useful in identifying chromosomal partners involved in unbalanced translocations and in revealing greater complexity of 13q rearrangements. Most of the newly identified or refined recurrent alterations involved 1q, 13q and 3q (gains/losses), 7q and 18q (gains), or 6q (losses), suggesting that these secondary aberrations may play a role in lymphomagenesis. Several patterns of genomic aberrations were identified: 1q gains in BL, trisomies 7 in DLBCL, and 18q-translocations in adult non-BL. BCP-ALL usually displayed an 18q21 rearrangement. BL karyotypes were less complex and aneuploid than those of other MYC-rearranged lymphomas. BCP-ALL and DLBCL/BL were associated with a higher rate of early death than BL and DLBCL. These findings support the categorization of DLBCL/BL as a distinct entity and suggest that BL with CK are indeed different from other aggressive MYC-rearranged lymphomas, which usually show greater genetic complexity. © 2012 Wiley Periodicals, Inc.

Characterization of novel genomic alterations and therapeutic approaches using acute megakaryoblastic leukemia xenograft models.

Acute megakaryoblastic leukemia (AMKL) is a heterogeneous disease generally associated with poor prognosis. Gene expression profiles indicate the existence of distinct molecular subgroups, and several genetic alterations have been characterized in the past years, including the t(1;22)(p13;q13) and the trisomy 21 associated with GATA1 mutations. However, the majority of patients do not present with known mutations, and the limited access to primary patient leukemic cells impedes the efficient development of novel therapeutic strategies. In this study, using a xenotransplantation approach, we have modeled human pediatric AMKL in immunodeficient mice. Analysis of high-throughput RNA sequencing identified recurrent fusion genes defining new molecular subgroups. One subgroup of patients presented with MLL or NUP98 fusion genes leading to up-regulation of the HOX A cluster genes. A novel CBFA2T3-GLIS2 fusion gene resulting from a cryptic inversion of chromosome 16 was identified in another subgroup of 31% of non-Down syndrome AMKL and strongly associated with a gene expression signature of Hedgehog pathway activation. These molecular data provide useful markers for the diagnosis and follow up of patients. Finally, we show that AMKL xenograft models constitute a relevant in vivo preclinical screening platform to validate the efficacy of novel therapies such as Aurora A kinase inhibitors.

PICALM-MLLT10 acute myeloid leukemia: a French cohort of 18 patients.

The PICALM-MLLT10 fusion gene, generated by the t(10;11)(p12-13;q14-21) translocation, is a rare but recurrent event in acute leukemias. In this study, we assessed the characteristics and outcome of 18 PICALM-MLLT10 AML patients. As compared with non PICALM-MLLT10 patients (n=72), PICALM-MLLT10 AML were characterized by more frequent extramedullary diseases, CD7 expression and higher platelet counts. Three out of four therapy-related PICALM-MLLT10 AMLs had been previously treated for diffuse large B-cell lymphoma. The complete response rate was 71% after intensive chemotherapy. PICALM-MLLT10 patients had a shorter median overall survival than patients with favorable cytogenetics (12 months vs. not reached, p=0.07) but not significantly different from those of intermediate (26 months, p=0.32) or unfavorable cytogenetic groups (8 months, p=0.13). Long term responses were achieved in a subset of patients after allogeneic stem-cell transplantation but also after high-dose cytarabine.

Functional analysis of the NUP98-CCDC28A fusion protein.

BACKGROUND: The nucleoporin gene NUP98 is rearranged in more than 27 chromosomal abnormalities observed in childhood and adult, de novo and therapy-related acute leukemias of myeloid and T-lymphoid origins, resulting in the creation of fusion genes and the expression of chimeric proteins. We report here the functional analysis of the NUP98-coiled-coil domain-containing protein 28A (NUP98-CCDC28A) fusion protein, expressed as the consequence of a recurrent t(6;11)(q24.1;p15.5) translocation. DESIGN AND METHODS: To gain insight into the function of the native CCDC28A gene, we collected information on any differential expression of CCDC28A among normal hematologic cell types and within subgroups of acute leukemia. To assess the in vivo effects of the NUP98-CCDC28A fusion, NUP98-CCDC28A or full length CCDC28A were retrovirally transduced into primary murine bone marrow cells and transduced cells were next transplanted into sub-lethally irradiated recipient mice. RESULTS: Our in silico analyses supported a contribution of CCDC28A to discrete stages of murine hematopoietic development. They also suggested selective enrichment of CCDC28A in the French-American-British M6 class of human acute leukemia. Primary murine hematopoietic progenitor cells transduced with NUP98-CCDC28A generated a fully penetrant and transplantable myeloproliferative neoplasm-like myeloid leukemia and induced selective expansion of granulocyte/macrophage progenitors in the bone marrow of transplanted recipients, showing that NUP98-CCDC28A promotes the proliferative capacity and self-renewal potential of myeloid progenitors. In addition, the transformation mediated by NUP98-CCDC28A was not associated with deregulation of the Hoxa-Meis1 pathway, a feature shared by a diverse set of NUP98 fusions. CONCLUSIONS: Our results demonstrate that the recurrent NUP98-CCDC28A is an oncogene that induces a rapid and transplantable myeloid neoplasm in recipient mice. They also provide additional evidence for an alternative leukemogenic mechanism for NUP98 oncogenes.

Chronic lymphocytic leukemia and prolymphocytic leukemia with MYC translocations: a subgroup with an aggressive disease course.

Translocations involving MYC are rare in chronic lymphocytic leukemia (CLL), and up to now, their prognostic significance remains unclear. We report the characteristics of 21 patients with CLL and nine patients with prolymphocytic leukemia (PLL), diagnosed in multiple centers (n = 13), which showed an MYC translocation demonstrated by fluorescence in situ hybridization. The prevalence was estimated to be <1%. Advanced age and male predominance were observed. Morphological analysis frequently revealed the presence of prolymphocytes. A typical "CLL-immunophenotype" was found in four of nine cases with PLL. Moreover, CD5 and CD23 were frequently expressed in PLL. The latter findings are atypical for PLL and may suggest transformation or progression of an underlying CLL. MYC translocations were frequently observed with concomitant adverse cytogenetic markers, such as del(11q) (n = 8/30) and/or del(17p)/monosomy 17 (n = 7/30). In addition, the presence of unbalanced translocations (n = 24 in 13/30 cases) and complex karyotype (n = 16/30) were frequent in cases with MYC translocations. Altogether, del(17p)/monosomy 17, del(11q), and/or complex karyotype were observed in 22 of 30 patients. Survival outcome was poor: the median time to treatment was only 5 months, and overall survival (OS) from clinical diagnosis and from genetic detection was 71 and 19 months, respectively. In conclusion, CLL/PLL with MYC translocations is a rare entity, which seems to be associated with adverse prognostic features and unfavorable outcome.

Refinement of 1p36 alterations not involving PRDM16 in myeloid and lymphoid malignancies.

Fluorescence in situ hybridization was performed to characterize 81 cases of myeloid and lymphoid malignancies with cytogenetic 1p36 alterations not affecting the PRDM16 locus. In total, three subgroups were identified: balanced translocations (N = 27) and telomeric rearrangements (N = 15), both mainly observed in myeloid disorders; and unbalanced non-telomeric rearrangements (N = 39), mainly observed in lymphoid proliferations and frequently associated with a highly complex karyotype. The 1p36 rearrangement was isolated in 12 cases, mainly myeloid disorders. The breakpoints on 1p36 were more widely distributed than previously reported, but with identifiable rare breakpoint cluster regions, such as the TP73 locus. We also found novel partner loci on 1p36 for the known multi-partner genes HMGA2 and RUNX1. We precised the common terminal 1p36 deletion, which has been suggested to have an adverse prognosis, in B-cell lymphomas [follicular lymphomas and diffuse large B-cell lymphomas with t(14;18)(q32;q21) as well as follicular lymphomas without t(14;18)]. Intrachromosomal telomeric repetitive sequences were detected in at least half the cases of telomeric rearrangements. It is unclear how the latter rearrangements occurred and whether they represent oncogenic events or result from chromosomal instability during oncogenesis.

Do AML patients with DNMT3A exon 23 mutations benefit from idarubicin as compared to daunorubicin? A single center experience.

Mutations in DNMT3A encoding DNA methyltransferase 3A were recently described in patients with acute myeloid leukemia. To assess their prognostic significance, we determined the mutational status of DNMT3A exon 23 in 288 patients with AML excluding acute promyelocytic leukemia, aged from 18 to 65 years and treated in Toulouse University Hospital. A mutation was detected in 39 patients (13.5%). All DNMT3A exon 23+ patients had intermediate-risk cytogenetics. Mutations significantly correlated with a higher WBC count (p less than 0.001), NPM1 and FLT3-ITD mutations (p=0.027). DNMT3A mutations were conserved through xenotransplantation in immunodeficient mice. No difference in outcome between DNMT3A exon 23+ and DNMT3A exon 23- patients was found even if the results were stratified by NPM1 or FLT3-ITD status. However, DNMT3A exon 23+ patients had better median DFS (not reached vs 11.6 months, p=0.009) and OS (not reached vs 14.3 months, p=0.005) as compared to DNMT3A exon 23- patients when treated with idarubicin, whereas patients treated with daunorubicin had similar outcome regardless the DNMT3A status. This study shows that DNMT3A mutations have no impact on outcome but could be a predictive factor for response to idarubicin and thus, could have a direct influence in the way AML patients should be managed.

EVI1-mediated down regulation of MIR449A is essential for the survival of EVI1 positive leukaemic cells.

Chromosomal rearrangements involving the MECOM (MDS1 and EVI1 complex) locus are recurrent genetic events in myeloid leukaemia and are associated with poor prognosis. In this study, we assessed the role of MECOM locus protein EVI1 in the transcriptional regulation of microRNAs (miRNAs) involved in the leukaemic phenotype. For this, we profiled expression of 366 miRNAs in 38 MECOM-rearranged patient samples, normal bone marrow controls and MECOM (EVI1) knock down/re-expression models. Cross-comparison of these miRNA expression profiling data showed that MECOM rearranged leukaemias are characterized by down regulation of MIR449A. Reconstitution of MIR449A expression in MECOM-rearranged cell line models induced apoptosis resulting in a strong decrease in cell viability. These effects might be mediated in part by MIR449A regulation of NOTCH1 and BCL2, which are shown here to be bona fide MIR449A targets. Finally, we confirmed that MIR449A repression is mediated through direct promoter occupation of the EVI1 transcriptional repressor. In conclusion, this study reveals MIR449A as a crucial direct target of the MECOM locus protein EVI1 involved in the pathogenesis of MECOM-rearranged leukaemias and unravels NOTCH1 and BCL2 as important novel targets of MIR449A. This EVI1-MIR449A-NOTCH1/BCL2 regulatory axis might open new possibilities for the development of therapeutic strategies in this poor prognostic leukaemia subgroup.

Identification of a transforming MYB-GATA1 fusion gene in acute basophilic leukemia: a new entity in male infants.

Acute basophilic leukemia (ABL) is a rare subtype of acute leukemia with clinical features and symptoms related to hyperhistaminemia because of excessive growth of basophils. No known recurrent cytogenetic abnormality is associated with this leukemia. Rare cases of t(X;6)(p11;q23) translocation have been described but these were sporadic. We report here 4 cases of ABL with a t(X;6)(p11;q23) translocation occurring in male infants. Because of its location on chromosome 6q23, MYB was a good candidate gene. Our molecular investigations, based on fluorescence in situ hybridization and rapid amplification of cDNA ends, revealed that the translocation generated a MYB-GATA1 fusion gene. Expression of MYB-GATA1 in mouse lineage-negative cells committed them to the granulocyte lineage and blocked at an early stage of differentiation. Taken together, these results establish, for the first time, a link between a recurrent chromosomal translocation and the development of this particular subtype of infant leukemia.

Specific chromosomal IG translocations have different prognoses in chronic lymphocytic leukemia.

BACKGROUND: Chromosomal translocations are usually analyzed as a single entity, and are associated with a poor outcome in chronic lymphocytic leukemia. Translocations involving immunoglobulin genes are recurrent, but uncommon (<5%), and their individual prognosis is not clear. The two most frequent partners are BCL2 (18q21) and BCL3 (19q13). DESIGNS AND METHODS: Herein, 75 cases are reported of chronic lymphocytic leukemia and t(14;18) (BCL2-CLLs). Our series benefits from morphological, immunological and cytogenetical reviews. The IGHV status analyses were performed by referring laboratories. Comparison was made with our previously published series of chronic lymphocytic leukemia patients with t(14;19) (BCL3-CLLs, n=29). RESULTS: Compared with BCL3-CLLs, lymphocytosis was lower in BCL2-CLLs (p<0.008), and splenomegaly was less frequent (p<0.0001). There were more "typical" morphologies (p<0.005) and Matutes scores >4 (p<0.001) in the BCL2-CLLs group, and less CD38 expression (p<0.04). More variant BCL2-translocations were observed (t(18;22), n=11; 2t(2;18), n=2; p<0.02), and BCL2-translocation was frequently single (p<0.002). Complex karyotypes (p<0.02), trisomy 12 (p<0.03), 6q deletion (p<0.002) and TP53 deletion (p<0.02) were less frequent in BCL2-CLLs, whereas 13q deletion was more frequent (p<0.005). The IGHV gene was frequently mutated in BCL2-CLLs (p<0.0001). Treatment-free survival was longer in BCL2-CLLs (p<0.0001). CONCLUSIONS: BCL2-CLL.S express CD5 and lack expression of CD38, and have a Matutes score ≥4, frequent trisomy 12, no ATM and 6q deletions, and a mutated IGHV status. Compared to BCL3-CLLs, BCL2-CLLs are much less aggressive; indicating that identifying individual translocations and cytogenetic partners would allow improved patient stratification.

The TLX1 oncogene drives aneuploidy in T cell transformation.

The TLX1 oncogene (encoding the transcription factor T cell leukemia homeobox protein-1) has a major role in the pathogenesis of T cell acute lymphoblastic leukemia (T-ALL). However, the specific mechanisms of T cell transformation downstream of TLX1 remain to be elucidated. Here we show that transgenic expression of human TLX1 in mice induces T-ALL with frequent deletions and mutations in Bcl11b (encoding B cell leukemia/lymphoma-11B) and identify the presence of recurrent mutations and deletions in BCL11B in 16% of human T-ALLs. Most notably, mouse TLX1 tumors were typically aneuploid and showed a marked defect in the activation of the mitotic checkpoint. Mechanistically, TLX1 directly downregulates the expression of CHEK1 (encoding CHK1 checkpoint homolog) and additional mitotic control genes and induces loss of the mitotic checkpoint in nontransformed preleukemic thymocytes. These results identify a previously unrecognized mechanism contributing to chromosomal missegregation and aneuploidy active at the earliest stages of tumor development in the pathogenesis of cancer.

Chromosomal abnormalities in transformed Ph-negative myeloproliferative neoplasms are associated to the transformation subtype and independent of JAK2 and the TET2 mutations.

Evolution to myelofibrosis (MF), acute myeloid leukemia or myelodysplastic syndrome (AML/MDS) may occur over time in myeloproliferative neoplasms (MPN) patients most likely due to the acquisition of additional mutations. The Groupe Francophone de cytogenetique hematologique (GFCH) has collected and reviewed 82 patients with transformation of MPN (66 AML/MDS and 16 MF). JAK2V617F and TET2 mutations were searched for in 40 and 32 patients, respectively. Significantly more -7/del(7q) (P = 0.004) and -5/del(5q) (P = 0.03) were found in AML/MDS with a higher incidence of dup1q (P = 0.01) in MF. Some specific chromosomal abnormalities occurred together, for example -5/del(5q) and -17/del(17p) (P = 0.0007). In multivariate analysis, two factors were independently associated with an inferior overall survival (OS); AML/MDS transformation (P < 0.0001) and -5/del(5q) abnormality (P = 0.02). Although both giving rise to loss of 7q, der(1;7) differed from other 7q deletions in terms of distribution (lower frequency of AML/MDS, P = 0.02), association with chromosomal abnormalities (absence of -5/del(5q), P = 0.003; increased del(20q), P = 0.05), and longer OS (P = 0.0007). We detected 24/40 (60%) JAK2V617F and 8/25 (32%) TET2 mutations in samples following transformation, ranging from wild-type to mutated forms of both genes. The mutated and wild-type forms of the genes were not found to be associated with a specific chromosomal abnormality. There was no evidence that JAK2 or TET2 mutations were associated with the type of MPN transformation, whereas the type of cytogenetic abnormalities were strongly linked, perhaps indicating that they play a specific role in the transformation process.