Childhood near-tetraploid acute lymphoblastic leukemia: an EGIL study on 36 cases

Integrated multi-omics analyses reveal homology-directed repair pathway as a unique dependency in near-haploid leukemia

Whole chromosome losses resulting in near-haploid karyotypes are found in a rare subgroup of treatment-refractory acute lymphoblastic leukemia. To systematically dissect the unique physiology and uncover susceptibilities that can be exploited in near-haploid leukemia, we leveraged single-cell RNA-Seq and computational inference of cell cycle stages to pinpoint key differences between near-haploid and diploid leukemia cells. Combining cell cycle stage-specific differential expression with gene essentiality scores from a genome-wide CRISPR-Cas9-mediated knockout screen, we identified the homologous recombination pathway component RAD51B as an essential gene in near-haploid leukemia. DNA damage analyses revealed significantly increased sensitivity of RAD51-mediated repair to RAD51B loss in the G2/M stage of near-haploid cells, suggesting a unique role of RAD51B in the homologous recombination pathway. Elevated G2/M and G1/S checkpoint signaling was part of a RAD51B signature expression program in response to chemotherapy in a xenograft model of human near-haploid B-ALL, and RAD51B and its associated programs were overexpressed in a large panel of near-haploid B-ALL patients. These data highlight a unique genetic dependency on DNA repair machinery in near-haploid leukemia and demarcate RAD51B as a promising candidate for targeted therapy in this treatment-resistant disease.

Overview on Aneuploidy in Childhood B-Cell Acute Lymphoblastic Leukemia

Recent years have brought significant progress in the treatment of B-cell acute lymphoblastic leukemia (ALL). This was influenced by both the improved schemes of conventionally used therapy, as well as the development of new forms of treatment. As a consequence, 5-year survival rates have increased and now exceed 90% in pediatric patients. For this reason, it would seem that everything has already been explored in the context of ALL. However, delving into its pathogenesis at the molecular level shows that there are many variations that still need to be analyzed in more detail. One of them is aneuploidy, which is among the most common genetic changes in B-cell ALL. It includes both hyperdiploidy and hypodiploidy. Knowledge of the genetic background is important already at the time of diagnosis, because the first of these forms of aneuploidy is characterized by a good prognosis, in contrast to the second, which is in favor of an unfavorable course. In our work, we will focus on summarizing the current state of knowledge on aneuploidy, along with an indication of all the consequences that may be correlated with it in the context of the treatment of patients with B-cell ALL.

Acute undifferentiated leukemia limited to neck lymph nodes and a large mediastinal mass

In the 2016 update of the World Health Organization (WHO) classification of myeloid neoplasms, acute undifferentiated leukemia (AUL) was defined by a lack of lineage-specific markers. AUL has very poor prognosis and no established therapies due to its rarity. We report a case of a 31-year-old man with AUL who showed complete molecular response to an acute lymphoblastic leukemia (ALL)-based regimen and received allogeneic hematopoietic stem cell transplantation. The patient's blast cells were CD7-positive and localized to lymph nodes in the neck and to a large mediastinal mass; there was also rearrangement of the T-cell receptor delta locus. Although the tumor showed characteristics of T-cell lymphoblastic lymphoma, it was categorized as AUL based on WHO classification. This case suggests that a high-intensity conditioning regimen could be effective for rare cases of AUL that present only in the extramedullary mass, and chemotherapy for AUL should be selected based on the characteristics of the blasts.

Near-tetraploid T-cell acute lymphoblastic leukaemia in childhood: Results of the AIEOP-BFM ALL studies

BACKGROUND

Near-tetraploidy-defined by DNA index 1.79-2.28 or 81-103 chromosomes-is a rare cytogenetic abnormality observed both in children and adults with T-cell acute lymphoblastic leukaemia (T-ALL) and its prognostic value is not yet determined.

PATIENTS AND METHODS

We report a retrospective study conducted in paediatric patients with newly diagnosed T-ALL treated in AIEOP-BFM ALL 2000 and 2009 studies. 31 near-tetraploid T-ALL patients (1.4%) are compared to T-ALL patients without near-tetraploidy.

RESULTS

Near-tetraploid karyotype was associated with lower frequency of high-risk features: white blood cells count at diagnosis ≥100,000/μL (19.3% versus 41.0%, p-value < 0.001), PPR (13.3% versus 35.8%, p-value = 0.01) and minimal residual disease high-risk at the end of consolidation phase Induction B (4.03% versus 14.6%, p-value = 0.001). Complete remission was achieved at the end of induction phase (day 33) in 100% near-tetraploid T-ALL patients, compared to 93.2% T-ALL without near-tetraploidy.

CONCLUSION

Overall, we found that near-tetraploid T-ALL in newly diagnosed paediatric patients is associated with low-risk presenting features, with favourable treatment response and outcome.

Pediatric T-cell acute lymphoblastic leukemia

The most common pediatric malignancy is acute lymphoblastic leukemia (ALL), of which T-cell ALL (T-ALL) comprises 10-15% of cases. T-ALL arises in the thymus from an immature thymocyte as a consequence of a stepwise accumulation of genetic and epigenetic aberrations. Crucial biological processes, such as differentiation, self-renewal capacity, proliferation, and apoptosis, are targeted and deranged by several types of neoplasia-associated genetic alteration, for example, translocations, deletions, and mutations of genes that code for proteins involved in signaling transduction, epigenetic regulation, and transcription. Epigenetically, T-ALL is characterized by gene expression changes caused by hypermethylation of tumor suppressor genes, histone modifications, and miRNA and lncRNA abnormalities. Although some genetic and gene expression patterns have been associated with certain clinical features, such as immunophenotypic subtype and outcome, none has of yet generally been implemented in clinical routine for treatment decisions. The recent advent of massive parallel sequencing technologies has dramatically increased our knowledge of the genetic blueprint of T-ALL, revealing numerous fusion genes as well as novel gene mutations. The challenges now are to integrate all genetic and epigenetic data into a coherent understanding of the pathogenesis of T-ALL and to translate the wealth of information gained in the last few years into clinical use in the form of improved risk stratification and targeted therapies. Here, we provide an overview of pediatric T-ALL with an emphasis on the acquired genetic alterations that result in this disease. © 2016 Wiley Periodicals, Inc.

Cytogenetic and Molecular Findings in Children with Acute Lymphoblastic Leukemia: Experience of a Single Institution in Argentina

The purpose of the current study was to evaluate the cytogenetic findings in 1,057 children with acute lymphoblastic leukemia (ALL) referred to the cytogenetics laboratory at the Hospital de Pediatría Dr. Juan P. Garrahan, between 1991 and 2014. Chromosomal abnormalities were evaluated by G-banding and FISH. Since December 2002, RT-PCR determinations were systematically carried out for BCR-ABL1, KMT2A-AFF1, ETV6-RUNX1, and TCF3-PBX1 rearrangements in children, adding KMT2A-MLLT3 and KMT2A-MLLT1 in infants. The percentage of abnormalities detected by cytogenetics was 70.1%. Four novel abnormalities, t(2;8)(p11.2;p22), inv(4)(p16q25), t(1;7)(q25;q32), and t(5;6)(q21;q21), were found in this cohort. We compared cytogenetic and RT-PCR results for BCR-ABL1, KMT2A-AFF1 and TCF3-PBX1 rearrangements in 497 children evaluated by both methods. The results were highly concordant (p < 0.7), and interestingly, FISH was relevant to confirm G-banding findings that were discordant with RT-PCR studies. This study showed the importance of performing G-banding, FISH and RT-PCR simultaneously to improve the detection of chromosomal abnormalities considering their important value in the diagnosis and prognosis of childhood ALL patients. Finally, to the best of our knowledge, this is the first series of cytogenetic findings in children with ALL reported in Argentina.

Prognostification of ALL by Cytogenetics

Cytogenetic abnormalities in chromosomal number and structure are common in pediatric ALL and some have prognostic significance. One interesting association between cytogenetic status and treatment response involves the metabolism of methotrexate. Hyperdiploid lymphoblasts accumulate increased amounts of MTX and MTX polyglutamates, and they have higher basal apoptotic rates compared with leukemic cells with lower ploidy and normal cells. These characteristics may contribute to the better outcomes observed for patients with hyperdiploid lymphoblasts. A number of recurrent chromosomal abnormalities have been shown to have prognostic significance, especially in B-precursor ALL. Some chromosomal abnormalities are associated with more favorable outcomes, such as high hyperdiploidy (51-65 chromosomes) and the ETV6-RUNX1 fusion. Others are associated with a poorer prognosis, including the Philadelphia chromosome [t(9;22)], rearrangements of the MLL gene (chromosome 11q23), and intrachromosomal amplification of the AML1 gene (iAMP21).

Acute leukemias of ambiguous origin

OBJECTIVES

This session of the Society for Hematopathology/European Association for Haematopathology Workshop focused on acute leukemias of ambiguous origin.

METHODS

We provide an overview of mixed-phenotype acute leukemia (MPAL) as recognized in the current World Health Organization classification and summarize diagnostic criteria for major categories of MPAL: B/myeloid, T/myeloid, B/T, and B/T/myeloid.

RESULTS

Most MPAL cases submitted were B/myeloid and T/myeloid MPAL, the most frequent types, but three cases of B/T MPAL were also submitted, and examples of all categories are illustrated. We emphasize that a comprehensive approach to immunophenotyping is required to accurately establish the diagnosis of MPAL. Flow cytometry immunophenotyping using a large panel of antibodies is needed as well as confirmatory immunohistochemical analysis and cytochemistry studies for myeloperoxidase and nonspecific esterase. We discuss technical issues in determining blast lineage and possible pitfalls in MPAL diagnosis. In particular, rare cases of B-acute lymphoblastic leukemia (B-ALL) can express myeloperoxidase but are otherwise consistent with B-ALL and should be treated as such. Last, we review the differential diagnosis between acute undifferentiated leukemia and acute myeloid leukemia with minimal differentiation.

CONCLUSIONS

There was an agreement that diagnosis of MPAL can be challenging, especially if applied flow cytometry panels are not comprehensive enough.

An unusual T-cell childhood acute lymphoblastic leukemia harboring a yet unreported near-tetraploid karyotype

BACKGROUND

Near-tetraploid (model #81-103) and near-triploid (model #67-81) karyotypes are found in around 1% of childhood acute lymphoblastic leukemia. Due to its rarity, these two cytogenetic subgroups are generally included in the hyperdiploid group (model # > 51). Therefore separate informations about these two subgroups are limited to a few reports. Some studies found that near-tetraploidy is relatively more frequent in higher median ages and it is associated to Frech-American-British Classification subtype L2. Although the mechanisms by which leukemic blast cells divide is still unclear, studies have suggested that hyperdiploidy, near-triploidy and near-tetraploidy do not seem to share the same mechanism.

FINDINGS

Herewith, we present a new childhood T-acute lymphoblastic leukemia case of near-tetraploid karyotype with loss of two p53-gene copies, characterized in detail by cytogenetic and molecular studies.

CONCLUSION

We suggest that p53 is a good target gene to be screened, once p53 is one of the main effectors of cell cycle checkpoints.