Is t(6;14) a non-random translocation in childhood acute mixed lineage leukemia?

Redefining the biological basis of lineage-ambiguous leukemia through genomics: BCL11B deregulation in acute leukemias of ambiguous lineage

Acute leukemias of ambiguous lineage (ALAL), including mixed phenotype acute leukemia (MPAL) and related entities such as early T-cell precursor acute leukemia (ETP-ALL), remain diagnostic and clinical challenges due to limited understanding of pathogenesis, reliance of immunophenotyping to classify disease, and the lack of a rational approach to guide selection of appropriate therapy. Recent studies utilizing genomic sequencing and complementary approaches have provided key insights that are changing the way in which such leukemias are classified, and potentially, treated. Several recurrent genomic alterations define leukemias that straddle immunophenotypic entities, such as ZNF384-rearranged childhood B-ALL and B/myeloid MPAL, and BCL11B-rearranged T/myeloid MPAL, ETP-ALL and AML. In contrast, some cases of MPAL represent canonical ALL/AML entities exhibiting lineage aberrancy. For many cases of ALAL, experimental approaches indicate lineage aberrancy arises from acquisition of a founding genetic alteration into a hematopoietic stem or progenitor cell. Determination of optimal therapeutic approach requires genomic characterization of uniformly treated ALAL patients in prospective studies, but several approaches, including kinase inhibitors and BH3 mimetics may be efficacious in subsets of ALAL.

Genomic characterization of chromosome translocations in patients with T/myeloid mixed-phenotype acute leukemia

Mixed-phenotype acute leukemia (MPAL) is a progenitor type of leukemia with ambiguous expression of lineage markers. The diagnosis of MPAL is based on flow cytometric analysis of immunophenotype, which commonly identifies myeloid lineage markers as well as B- or T- lymphoid lineage markers on leukemic blasts. Due to the rare occurrence of this disease, few studies have delineated the molecular bases of MPAL. Combining conventional karyotyping with whole genomic sequencing (WGS) and RNA sequencing (RNA-seq), we report here our identification and characterization of chromosome translocations, gene mutations and gene expression profile in four patients with T/Myeloid MPAL, including two t(6;14)(q25;q32) one t(8;14)(q24.2;q32) and one t(7;8)(p14;q24.2). Notably, seven of the eight translocation breakpoints reside in the non-coding regions and their locations appear to be shared by two or more patients. Gene expression analysis of matched diagnostic vs. remission samples provided evidence of transcriptomes alteration involving nucleosome organization and chromatin assembly.

Integrated genome-wide genotyping and gene expression profiling reveals BCL11B as a putative oncogene in acute myeloid leukemia with 14q32 aberrations

Acute myeloid leukemia is a neoplasm characterized by recurrent molecular aberrations traditionally demonstrated by cytogenetic analyses. We used high density genome-wide genotyping and gene expression profiling to reveal acquired cryptic abnormalities in acute myeloid leukemia. By genome-wide genotyping of 137 cases of primary acute myeloid leukemia, we disclosed a recurrent focal amplification on chromosome 14q32, which included the genes BCL11B, CCNK, C14orf177 and SETD3, in two cases. In the affected cases, the BCL11B gene showed consistently high mRNA expression, whereas the expression of the other genes was unperturbed. Fluorescence in situ hybridization on 40 cases of acute myeloid leukemia with high BCL11B mRNA expression [2.5-fold above median; 40 out of 530 cases (7.5%)] revealed 14q32 abnormalities in two additional cases. In the four BCL11B-rearranged cases the 14q32 locus was fused to different partner chromosomes. In fact, in two cases, we demonstrated that the focal 14q32 amplifications were integrated into transcriptionally active loci. The translocations involving BCL11B result in increased expression of full-length BCL11B protein. The BCL11B-rearranged acute myeloid leukemias expressed both myeloid and T-cell markers. These biphenotypic acute leukemias all carried FLT3 internal tandem duplications, a characteristic marker of acute myeloid leukemia. BCL11B mRNA expression in acute myeloid leukemia appeared to be strongly associated with expression of other T-cell-specific genes. Myeloid 32D(GCSF-R) cells ectopically expressing Bcl11b showed decreased proliferation rate and less maturation. In conclusion, by an integrated approach involving high-throughput genome-wide genotyping and gene expression profiling we identified BCL11B as a candidate oncogene in acute myeloid leukemia.

AML1/RUNX1 gene point mutations in childhood myeloid malignancies

BACKGROUND

Currently, it is widely accepted that one of the crucial players in adult leukemic transformation is the RUNX1 gene. However, there is little data available regarding whether mutations in this gene also contribute to pediatric leukemia, especially in childhood myeloid malignancies. Therefore we made a decision to screen patients with pediatric myeloid neoplasias for the presence of RUNX1 mutations in their samples.

PROCEDURES

Patients (n = 238) with diagnoses of de novo acute myeloid leukemia (AML) (n = 198), de novo myelodisplastic syndrome (MDS) (n = 16), therapy-related AML (n = 9), juvenile myelomonocytic leukemia (JMML) (n = 15) were included in this study. All patients were Belarusians between the ages of 0 and 18 years.

RESULTS

The frequency of RUNX1 point mutations in the total group of patients with de novo AML was 3% and de novo MDS was 15%. Cooperation of point mutations in the RUNX1 and NRAS genes, and the cytogenetic abnormality, -7/7q-, was demonstrated in children with therapy-related AML. RUNX1 point mutations predominate in those de novo AML and MDS patients with a normal karyotype in leukemic cells. Frequency of RUNX1 point mutations was about 4% in a group of children with de novo AML aged 0-14 years diagnosed during the period of 1998-2009.

CONCLUSION

During the course of this investigation, valuable data were obtained concerning RUNX1 gene mutation frequencies in different clinical, morphological, and cytogenetic groups of patients with myeloid malignancies, and its cooperation with other molecular aberrations.

A novel t(6;14)(q25-q27;q32) in acute myelocytic leukemia involves the BCL11B gene

Cytogenetic studies in a patient with acute myelocytic leukemia (AML) revealed as the sole karyotypic alteration a half-cryptic rearrangement, identified with 48-color combined binary ratio-labeled fluorescence in situ hybridization (pq-COBRA-FISH) as a reciprocal t(6;14)(q?;q?). The breakpoints were later assigned on the basis of G-banding to t(6;14)(q25-q26;q32). FISH experiments using genomic probes showed that the breakpoint on 14q32.2 was within bacterial artificial chromosome RP11-782I5 and revealed BCL11B as the only candidate gene in the region. BCL11B is a homolog to BCL11A (2p13), a highly conserved gene implicated in mouse and human leukemias. To our knowledge, this is the first report implicating BCL11B in hematological malignancies. Because of lack of material, the translocation partner remains unknown.

Marked thrombocytosis following relapse of acute myeloblastic leukemia associated with development of translocation (2;14) (p13;q32)

Thrombocytosis is a rare finding in acute myeloblastic leukemia (AML). Here, we describe a patient with AML who relapsed with marked thrombocytosis. The patient was initially diagnosed as having AML (M4) with a low platelet count. The patient was started on combination chemotherapy including high-dose etoposide and achieved complete remission. However, the patient relapsed six months later with an extremely high platelet count (72.5 x 10(4)/microl). Cytogenetic analysis at relapse revealed the development of t(2;14)(p13;q32). Despite the repeated combination chemotherapy, the patient died with progressive disease. This case suggests that the additional chromosomal aberration t(2;14)(p13;q32) may be related to abnormal thrombocytosis in AML.

Fusion of the Platelet-Derived Growth Factor Receptor β to a Novel Gene CEV14 in Acute Myelogenous Leukemia After Clonal Evolution

Chromosomal translocations involving band 5q31-35 occur in several hematologic disorders. A clone with a t(5; 14)(q33; q32) translocation appeared at the relapse phase in a patient with acute myelogenous leukemia who exhibited a sole chromosomal translocation, t(7; 11), at initial diagnosis. After the appearance of this clone, the leukemia progressed with marked eosinophilia, and combination chemotherapy was ineffective. Southern blot analysis showed a rearrangement of the platelet-derived growth factor receptor β (PDGFRβ) gene at 5q33 which was not observed at initial diagnosis. This translocation resulted in a chimeric transcript fusing the PDGFRβ gene on 5q33 with a novel gene, CEV14, located at 14q32. Expression of the 5′ region of the PDGFRβ cDNA, upstream of the breakpoint, was not detected. However, the 3′ region of PDGFRβ, which was transcribed as part of the CEV14-PDGFRβ fusion gene, was detected. A partial cDNA for a novel gene, CEV14, includes a leucine zipper motif and putative thyroid hormone receptor interacting domain and is expressed in a wide range of tissues. The expression of a CEV14-PDGFRβ fusion gene in association with aggressive leukemia progression suggests that this protein has oncogenic potential.

Fusion of the Platelet-Derived Growth Factor Receptor β to a Novel Gene CEV14 in Acute Myelogenous Leukemia After Clonal Evolution

Chromosomal translocations involving band 5q31-35 occur in several hematologic disorders. A clone with a t(5; 14)(q33; q32) translocation appeared at the relapse phase in a patient with acute myelogenous leukemia who exhibited a sole chromosomal translocation, t(7; 11), at initial diagnosis. After the appearance of this clone, the leukemia progressed with marked eosinophilia, and combination chemotherapy was ineffective. Southern blot analysis showed a rearrangement of the platelet-derived growth factor receptor β (PDGFRβ) gene at 5q33 which was not observed at initial diagnosis. This translocation resulted in a chimeric transcript fusing the PDGFRβ gene on 5q33 with a novel gene, CEV14, located at 14q32. Expression of the 5′ region of the PDGFRβ cDNA, upstream of the breakpoint, was not detected. However, the 3′ region of PDGFRβ, which was transcribed as part of the CEV14-PDGFRβ fusion gene, was detected. A partial cDNA for a novel gene, CEV14, includes a leucine zipper motif and putative thyroid hormone receptor interacting domain and is expressed in a wide range of tissues. The expression of a CEV14-PDGFRβ fusion gene in association with aggressive leukemia progression suggests that this protein has oncogenic potential.