Laboratory characterization of the pediatric B/T subtype of mixed-phenotype acute leukemia: Report of a case series.

OBJECTIVES: Mixed-phenotype acute leukemia (MPAL) is a rare disease associated with difficulties in the correct lineage assignment of leukemic cells. One of the least common subtypes within this category is characterized by the simultaneous presence of B- and T-lineage-defining antigens. Each case of suspected B/T MPAL should be considered in light of all available laboratory and clinical data to avoid misdiagnosis. METHODS: In this study, we describe 6 pediatric patients who presented with leukemic blasts bearing B- and T-lineage antigens at diagnosis, including their clinical, immunophenotypic, morphologic, and cytogenetic characteristics. RESULTS: In 3 patients, more or less distinct populations of B- and T-lymphoid origin were found; the other 3 patients had a single mixed-phenotype blast population. All cases fulfilled the World Health Organization criteria, but not all of them turned out to be bona fide cases of B/T MPAL according to the available clinical and laboratory data. Found genetic lesions were helpful for the confirmation of MPAL instead of 2 concomitant tumors, but for a general B/T MPAL diagnosis, genetic studies provided the only descriptive data. CONCLUSIONS: The accurate diagnosis of B/T MPAL requires a multidisciplinary approach combining high-tech laboratory methods and close cooperation between treating physicians and pathologists.

Genetic characteristics and treatment outcome in infants with KMT2A germline B-cell precursor acute lymphoblastic leukemia: Results of MLL-Baby protocol.

The aim of this study was to present the diagnostic and outcome characteristics of infants with germline status of KMT2A gene (KMT2A-g) B-cell precursor acute lymphoblastic leukemia (BCP-ALL) treated consistently according to the MLL-Baby protocol, a moderate-intensity protocol. Of the 139 patients enrolled in the MLL-Baby study, 100 (71.9%) carried different types of rearranged KMT2A (KMT2A-r), while the remaining 39 infants (28.1%) had KMT2A-g. KMT2A-g patients were generally older (77% older than 6 months), less likely to have a very high white blood cell count (greater than 100 × 109 /L), less likely to be central nervous system (CNS)-positive, and more likely to be CD10-positive. The 6-year event-free survival and overall survival rates for all 39 patients were 0.74 (standard error [SE] 0.07) and 0.80 (SE 0.07), respectively. Relapse was the most common adverse event (n = 5), with a cumulative incidence of relapse (CIR) of 0.13 (SE 0.06), while the incidence of a second malignancy (n = 1) and death in remission (n = 3) was 0.03 (SE 0.04) and 0.08 (SE 0.04), respectively. None of the initial parameters, including genetics and the presence of recently described fusions of NUTM1 and PAX5 genes, was able to distinguish patients with different outcomes. Only rapidity of response, measured as minimal residual disease (MRD) by flow cytometry, showed a statistically significant impact. Moderate-intensity therapy, as used in the MLL-Baby protocol in infants with KMT2A-g BCP-ALL, yields results comparable to other infant studies. Patients with a slow multicolor flow cytometry (MFC)-MRD response should be subjected to advanced therapies, such as targeted or immunotherapies.

Comparison of minimal residual disease measurement by multicolour flow cytometry and PCR for fusion gene transcripts in infants with acute lymphoblastic leukaemia with KMT2A gene rearrangements.

This study aimed to evaluate the concordance between minimal residual disease (MRD) results obtained by multicolour flow cytometry (MFC) and polymerase chain reaction for fusion gene transcripts (FGTs) in infants with acute lymphoblastic leukaemia (ALL) associated with rearrangement of the KMT2A gene (KMT2A-r). A total of 942 bone marrow (BM) samples from 123 infants were studied for MFC-MRD and FGT-MRD. In total, 383 samples (40.7%) were concordantly MRD-negative. MRD was detected by the two methods in 441 cases (46.8%); 99 samples (10.5%) were only FGT-MRD-positive and 19 (2.0%) were only MFC-MRD-positive. A final concordance rate of 87.4% was established. Most discordance occurred if residual leukaemia was present at levels close to the sensitivity limits. Neither the type of KMT2A fusion nor a new type of treatment hampering MFC methodology had an influence on the concordance rate. The prognostic value of MFC-MRD and FGT-MRD differed. MFC-MRD was able to identify a rapid response at early time-points, whereas FGT-MRD was a reliable relapse predictor at later treatment stages. Additionally, the most precise risk definition was obtained when combining the two methods. Because of the high comparability in results, these two rather simple and inexpensive approaches could be good options of high clinical value.

Incidence and prognostic value of central nervous system involvement in infants with B-cell precursor acute lymphoblastic leukemia treated according to the MLL-Baby protocol.

AIM: The aim of the study was to evaluate the incidence and prognostic impact of central nervous system (CNS) involvement in infants with B-cell precursor acute lymphoblastic leukemia (BCP-ALL), as well as its relation with minimal residual disease (MRD) data. METHODS: A total of 139 consecutive infants with BCP-ALL from the MLL-Baby trial were studied. Cerebrospinal fluid (CSF) samples were investigated by microscopy of cytospin slides. MRD was evaluated according to the protocol schedule by flow cytometry and PCR for fusion gene transcripts (FGT). RESULTS: Involvement of the CNS at any level was found in 50 infants (36.0%). The incidence of CNS involvement was higher in patients with KMT2A gene rearrangements (44.0% for KMT2A-r vs. 15.4% for KMT2A-g, p = .003). The outcome of CNS-positive infants was significantly worse than that of CNS-negative infants, although this prognostic impact was limited to the KMT2A-r group (event-free survival 0.21 for CNS-positive vs. 0.48 for CNS-negative infants, p = .044). CNS-positive infants could not be treated successfully by conventional chemotherapy alone, irrespective of the rapidity of MRD response. In contrast, the combination of initial CNS negativity and FGT-MRD negativity identified a group comprising up to one-third of infants with KMT2A-r ALL who can be treated with chemotherapy and achieve very good outcomes (disease-free survival above 95%), and remaining patients should be allocated to receive other types of treatment. CONCLUSION: We can conclude that this combination of initial CNS involvement and MRD data can significantly improve risk-group allocation in future clinical trials enrolling infants with ALL.

Lineage Conversion in Pediatric B-Cell Precursor Acute Leukemia under Blinatumomab Therapy.

We report incidence and deep molecular characteristics of lineage switch in 182 pediatric patients affected by B-cell precursor acute lymphoblastic leukemia (BCP-ALL), who were treated with blinatumomab. We documented six cases of lineage switch that occurred after or during blinatumomab exposure. Therefore, lineage conversion was found in 17.4% of all resistance cases (4/27) and 3.2% of relapses (2/63). Half of patients switched completely from BCP-ALL to CD19-negative acute myeloid leukemia, others retained CD19-positive B-blasts and acquired an additional CD19-negative blast population: myeloid or unclassifiable. Five patients had KMT2A gene rearrangements; one had TCF3::ZNF384 translocation. The presented cases showed consistency of gene rearrangements and fusion transcripts across initially diagnosed leukemia and lineage switch. In two of six patients, the clonal architecture assessed by IG/TR gene rearrangements was stable, while in others, loss of clones or gain of new clones was noted. KMT2A-r patients demonstrated very few additional mutations, while in the TCF3::ZNF384 case, lineage switch was accompanied by a large set of additional mutations. The immunophenotype of an existing leukemia sometimes changes via different mechanisms and with different additional molecular changes. Careful investigation of all BM compartments together with all molecular -minimal residual disease studies can lead to reliable identification of lineage switch.

Prognostic value of minimal residual disease measured by fusion-gene transcript in infants with KMT2A-rearranged acute lymphoblastic leukaemia treated according to the MLL-Baby protocol.

The prognostic value of minimal residual disease (MRD) measured by fusion-gene transcript (FGT) detection was investigated in 76 infants (aged ≤1 year) with acute lymphoblastic leukaemia (ALL) with lysine methyltransferase 2A (KMT2A) rearrangements. Either at the end of induction or at later time-points, FGT-MRD-positivity was associated with poor outcome. FGT-MRD-positivity after first consolidation or first high-risk block detected 46·5% of infants with extremely poor outcome [disease-free survival (SE) 0·06 (0·06), cumulative incidence of relapse (SE) 0·91 (0·05)], which was also confirmed in multivariable analysis. Thus, FGT-MRD measurement at a single time-point clearly identifies infants with ALL who are curable with conventional chemotherapy and those who would benefit only from other treatment approaches.

Reduced vs. standard dose native E. coli-asparaginase therapy in childhood acute lymphoblastic leukemia: long-term results of the randomized trial Moscow-Berlin 2002.

PURPOSE: Favorable outcomes were achieved for children with acute lymphoblastic leukemia (ALL) with the first Russian multicenter trial Moscow-Berlin (ALL-MB) 91. One major component of this regimen included a total of 18 doses of weekly intramuscular (IM) native Escherichia coli-derived asparaginase (E. coli-ASP) at 10000 U/m2 during three consolidation courses. ASP was initially available from Latvia, but had to be purchased from abroad at substantial costs after the collapse of Soviet Union. Therefore, the subsequent trial ALL-MB 2002 aimed at limiting costs to a reasonable extent and also at reducing toxicity by lowering the dose for standard risk (SR-) patients to 5000 U/m2 without jeopardizing efficacy. METHODS: Between April 2002 and November 2006, 774 SR patients were registered in 34 centers across Russia and Belarus, 688 of whom were randomized. In arm ASP-5000 (n = 334), patients received 5000 U/m2 and in arm ASP-10000 (n = 354) 10 000 U/m2 IM. RESULTS: Probabilities of disease-free survival, overall survival and cumulative incidence of relapse at 10 years were comparable: 79 ± 2%, 86 ± 2% and 17.4 ± 2.1% (ASP-5000) vs. 75 ± 2% and 82 ± 2%, and 17.9 ± 2.0% (ASP-10000), while death in complete remission was significantly lower in arm ASP-5000 (2.7% vs. 6.5%; p = 0.029). CONCLUSION: Our findings suggest that weekly 5000 U/m2E. coli-ASP IM during consolidation therapy are equally effective, more cost-efficient and less toxic than 10000 U/m2 for SR patients with childhood ALL.