Autocrine stimulation of interleukin 1 beta in acute myelogenous leukemia cells.

A significant increase in CD25 antigen-positive cells by IL-1 was observed in cells of a patient with M7 acute myelogenous leukemia. Basal proliferation and expression of CD25 antigen by the M7 leukemic cells were inhibited by addition of anti-IL-1 beta antibody in a dose-dependent manner, but not by rabbit anti-IL-1 alpha antibody. Culture supernatants of these leukemic cells contained IL-1 activity, which was specifically inhibited by addition of anti-IL-1 beta antibody, and Northern blot analysis detected intracellular IL-1 beta mRNA. These results indicated that autocrine secretion of IL-1 beta was involved in proliferation of some myelogenous leukemic cells.

High-dose methotrexate therapy significantly improved survival of adult acute lymphoblastic leukemia: a phase III study by JALSG.

High-dose methotrexate (Hd-MTX) therapy has recently been applied to the treatment of adult acute lymphoblastic leukemia (ALL) based on pediatric protocols; however, its effectiveness for adult ALL has not yet been confirmed in a rigorous manner. We herein conducted a randomized phase III trial comparing Hd-MTX therapy with intermediate-dose (Id)-MTX therapy. This study was registered at UMIN-CTR (ID: C000000063). Philadelphia chromosome (Ph)-negative ALL patients aged between 25 and 64 years of age were enrolled. Patients who achieved complete remission (CR) were randomly assigned to receive therapy containing Hd-MTX (3 g/m2) or Id-MTX (0.5 g/m2). A total of 360 patients were enrolled. The CR rate was 86%. A total of 115 and 114 patients were assigned to the Hd-MTX and Id-MTX groups, respectively. The estimated 5-year disease-free survival rate of the Hd-MTX group was 58%, which was significantly better than that of the Id-MTX group at 32% (P=0.0218). The frequencies of severe adverse events were not significantly different. We herein demonstrated the effectiveness and safety of Hd-MTX therapy for adult Ph-negative ALL. Our results provide a strong rationale for protocols containing Hd-MTX therapy being applied to the treatment of adult ALL.

Synthesis of a novel cytokine and its gene (LD78) expressions in hematopoietic fresh tumor cells and cell lines.

The gene coding for the protein LD78 was isolated from stimulated human tonsillar lymphocytes by differential hybridization. The gene product consisted of 92 amino acids with characteristics of cytokines. LD78 gene transcripts were detected in eight of eight fresh samples of cells from patients with acute nonlymphocytic leukemia (ANLL) by Northern blot analysis. ANLL cells with monocytic features gave the strongest bands. RNA transcripts were found in two of three samples of cells from patients with adult T cell leukemia (ATL), eight of nine samples from patients with acute lymphocytic leukemia (ALL) of B cell lineage, and one of the three samples from patients with T cell ALL. KG-1, HL-60, HUT 102, MT-2, and MJ cell lines expressed the LD78 gene constitutively. The LD78 protein was detected in culture supernatants and cell lysates of HUT 102, MT-2, MJ, and fresh ATL cells by Western blot analysis. This protein was not found in culture supernatants or cell lysates of monocytic leukemia cells and HL-60 cells, although LD78 transcripts were found in those cells. The discrepancy between gene and protein expression might be explained by the stability of the mRNA. Thus, the protein may be involved in the neoplastic transformation of hematopoietic cells.

Frequent somatic mutations in epigenetic regulators in newly diagnosed chronic myeloid leukemia.

Although tyrosine kinase inhibitors (TKIs) have significantly improved the prognosis of chronic myeloid leukemia (CML), the ability of TKIs to eradicate CML remains uncertain and patients must continue TKI therapy for indefinite periods. In this study, we performed whole-exome sequencing to identify somatic mutations in 24 patients with newly diagnosed chronic phase CML who were registered in the JALSG CML212 study. We identified 191 somatic mutations other than the BCR-ABL1 fusion gene (median 8, range 1-17). Age, hemoglobin concentration and white blood cell counts were correlated with the number of mutations. Patients with mutations ⩾6 showed higher rate of achieving major molecular response than those<6 (P=0.0381). Mutations in epigenetic regulator, ASXL1, TET2, TET3, KDM1A and MSH6 were found in 25% of patients. TET2 or TET3, AKT1 and RUNX1 were mutated in one patient each. ASXL1 was mutated within exon 12 in three cases. Mutated genes were significantly enriched with cell signaling and cell division pathways. Furthermore, DNA copy number analysis showed that 2 of 24 patients had uniparental disomy of chromosome 1p or 3q, which disappeared major molecular response was achieved. These mutations may play significant roles in CML pathogenesis in addition to the strong driver mutation BCR-ABL1.

Mutations in the receptor tyrosine kinase pathway are associated with clinical outcome in patients with acute myeloblastic leukemia harboring t(8;21)(q22;q22).

AML1-MTG8 generated by t(8;21) contributes to leukemic transformation, but additional events are required for full leukemogenesis. We examined whether mutations in the receptor tyrosine kinase (RTK) pathway could be the genetic events that cause acute myeloblastic leukemia (AML) harboring t(8;21). Mutations in the second tyrosine kinase domain, juxtamembrane (JM) domain and exon 8 of the C-KIT gene were observed in 10, one and three of 37 AML patients with t(8;21), respectively. Three patients showed an internal tandem duplication in the JM domain of the FLT3 gene. One patient had a mutation in the K-Ras gene at codon 12. As the occurrence of these mutations was mutually exclusive, a total of 18 (49%) patients showed mutations in the RTK pathway. These results suggest that activating mutations in the RTK pathway play a role in part as an additional event leading to the development of t(8;21) AML. The 6-year cumulative incidence of relapse in patients with RTK pathway mutations was 79.8%, compared with 13.5% in patients lacking such mutations (P=0.0029). Furthermore, the 6-year relapse-free survival in patients with mutations was 18% compared to 60% in those without mutations (P=0.0340), indicating that RTK mutations are associated with the clinical outcome in t(8;21) AML.

Discordant gene and surface expression of the T-cell receptor/CD3 complex in adult T-cell leukemia cells.

Cell surface expression of the T-cell receptor (TCR)/CD3 complex on the cells from 11 acute type adult T-cell leukemia (ATL) and 4 lymphoma type ATL patients was examined by flow cytometry. Cells from 10 of 11 acute ATL patients were TCR alpha beta+ and CD3+, and their mean fluorescence intensities were low (TCR alpha beta, 25.3-84.6; CD3, 22.8-87.8). Cells from two of four lymphoma type ATL did not express this complex, and the other two were CD3+, TCR alpha beta-. In contrast, the mean fluorescence intensity of the TCR/CD3 complex in cells from a patient with T4 chronic lymphocytic leukemia was not low (TCR alpha beta, 129.9; CD3, 117.1). mRNA expressions of the TCR alpha, beta, and CD3 gamma, delta, epsilon, and zeta chains were examined by Northern blots. ATL cells from two acute and two lymphoma types expressed amounts of this complex equal to or greater than those expressed by T4 chronic lymphocytic leukemia. CD3 delta and TCR beta mRNA in ATL and T4 chronic lymphocytic leukemia cells were equally stable to actinomycin D treatment. The synthesis of CD3 zeta protein by ATL cells was detected by Western blotting assay. On the basis of these findings, we discuss the possible involvement of the TCR/CD3 complex in activation of ATL cells.

Human urinary macrophage colony-stimulating factor reduces the incidence and duration of febrile neutropenia and shortens the period required to finish three courses of intensive consolidation therapy in acute myeloid leukemia: a double-blind controlled study.

PURPOSE: To determine whether macrophage colony-stimulating factor (M-CSF) reduces the incidence and duration of febrile neutropenia during three courses of intensive consolidation therapy and whether it shortens time to complete consolidation therapy. PATIENTS AND METHODS: In 198 adult patients with acute myeloid leukemia (AML) in complete remission (CR), M-CSF (8 x 10(6) U/d) or placebo was administered from 1 day after the end of each consolidation chemotherapy for 14 days. RESULTS: The duration and incidence of febrile neutropenia was significantly reduced by 34% (P = .00285) and 17% (P = .02065), respectively, in 88 assessable patients in the M-CSF group compared with those in 94 assessable patients in the placebo group. Patients in the M-CSF group had 565 days and 133 episodes of febrile neutropenia during 7,901 days at risk, while patients in the placebo group had 977 days and 185 episodes during 9,077 days at risk. The median period required to finish the three courses of consolidation therapy was 93 days in the M-CSF group, which was significantly shorter than 110 days in placebo group (P = .0050). In the M-CSF group, the recovery of neutrophils and platelets was significantly faster (P = .0348 and P = 0.0364, respectively), the administration of systemic antimicrobial agents tended to be less (P = .0839), and the frequency of platelet transfusion (P = .0259) and the total volume of transfused platelets (P = .0292) were significantly less. However, there was no significant difference in the disease-free survival. CONCLUSION: M-CSF significantly reduced the incidence and duration of febrile neutropenia during the intensive consolidation therapy, and shortened the time to complete consolidation chemotherapy in AML.

Analysis of prognostic factors in newly diagnosed acute promyelocytic leukemia treated with all-trans retinoic acid and chemotherapy. Japan Adult Leukemia Study Group.

PURPOSE: We conducted a multicenter study of differentiation therapy with all-trans retinoic acid (ATRA) followed by intensive chemotherapy in patients with newly diagnosed acute promyelocytic leukemia (APL) and analyzed the prognostic factors for predicting complete remission (CR), event-free survival (EFS), and disease-free survival (DFS). PATIENTS AND METHODS: All patients received ATRA until CR. If patients had an initial leukocyte count greater than 3.0 x 10(9)/L, they received daunorubicin (DNR) and behenoyl cytarabine (BHAC). During therapy, if patients showed blast and promyelocyte counts greater than 1.0 x 10(9)/L, they received additional DNR and BHAC. After achieving CR, patients received three courses of consolidation and six courses of maintenance/intensification chemotherapy. RESULTS: Of 198 registered, 196 were assessable (age range, 15 to 86 years; median, 46) and 173 (88%) achieved CR. Multivariate analysis showed that no or minor purpura at diagnosis (P = .0046) and age less than 30 years (P = .0076) were favorable factors for achievement of CR. Predicted 4-year overall survival and EFS rates were 74% and 54%, respectively, and the 4-year predicted DFS rate for 173 CR patients was 62%. Multivariate analysis showed that age less than 30 years (P = .0003) and initial leukocyte count less than 10 x 10(9)/L (P = .0296) were prognostic factors for longer EFS, and initial leukocyte count less than 10.0 x 10(9)/L was a sole significant prognostic factor for longer DFS (P = .0001). CONCLUSION: Our results show that age, hemorrhagic diathesis, and initial leukocyte count are prognostic factors for APL treated with ATRA followed by intensive chemotherapy.

Randomized trials between behenoyl cytarabine and cytarabine in combination induction and consolidation therapy, and with or without ubenimex after maintenance/intensification therapy in adult acute myeloid leukemia. The Japan Leukemia Study Group.

PURPOSE: We analyzed complete remission (CR), disease-free survival (DFS), and event-free survival (EFS) rates in two groups of patients treated with either N4-behenoyl-1-beta-D-arabinosylcytosine (BHAC) or cytarabine, and analyzed DFS with or without ubenimex, a biologic response modifier. PATIENTS AND METHODS: Newly diagnosed patients with acute myeloid leukemia (AML) were randomized to receive either BHAC or cytarabine as remission-induction combination chemotherapy and two courses of consolidation therapy. After maintenance/intensification therapy, patients in CR were randomized to receive either ubenimex and no drug. RESULTS: Of 341 patients registered, 326 were assessable. The age of assessable patients ranged from 15 to 82 years (median, 48). The overall CR rate was 77%: 72% in the BHAC group and 81% in the cytarabine group, and there was a significant difference between the two groups (P = .035, chi 2 test). The predicted 55-month EFS rate of all patients was 30%: 23% in the BHAC group and 35% in the cytarabine group, with a significant difference between groups (P = .0253). The predicted 55-month DFS rate of all CR patients was 38% and that of CR patients less than 50 years of age was 47%. There was no significant difference in DFS between the ubenimex group and the group that did not receive ubenimex. CONCLUSION: Analyses of our clinical trial showed that the use of BHAC in remission-induction therapy and in consolidation therapy resulted in poorer CR and EFS rates in adult AML patients compared with the use of cytarabine at the doses and schedules tested. Immunotherapy with ubenimex after the end of all chemotherapy did not improve DFS.

Treatment of acute promyelocytic leukemia: strategy toward further increase of cure rate.

Acute promyelocytic leukemia (APL) has become a curable disease by all-trans retinoic acid (ATRA)-based induction therapy followed by two or three courses of consolidation chemotherapy. Currently around 90% of newly diagnosed patients with APL achieve complete remission (CR) and over 70% of patients are curable. To further increase the CR and cure rates, detection and diagnosis of this disease at its early stage is very important, hopefully before the appearance of APL-associated coagulopathy. In induction therapy, concomitant chemotherapy is indispensable, except for patients with low initial leukocyte counts. Prophylactic use of intrathecal methotrexate and cytarabine should be done, particularly for patients with hyperleukocytosis. If patients relapse hematologically or even molecularly, arsenic trioxide will be the treatment of choice under careful electrocardiogram monitoring. Am80, liposomal ATRA, gemtuzumab ozogamicin or ATRA in combination with cytotoxic drugs may be used at this stage or later. Allogeneic SCT will be the treatment of choice after patients of age <50 years have relapsed, provided that they have HLA-identical family donors or DNA-identical unrelated donors.

High degree of myeloid differentiation and granulocytosis is associated with t(8;21) smoldering leukemia.

The t(8;21) is a frequent chromosome abnormality in acute myeloid leukemia (AML), particularly associated with M2 of the French-American-British (FAB) classification, but also found in a few patients with myelodysplastic syndrome (MDS). The two genes involved in the t(8;21) have been recently isolated and the cDNA of the AML1/ETO fusion gene identified. We have investigated a series of AML and MDS patients by a reverse transcriptase-polymerase chain reaction (RT-PCR) and analyzed the clinical and laboratory features of leukemia with t(8;21). The t(8;21) was only found in a subset of M2, which had the clinical and hematological features distinct from those M2 without t(8;21). M2 with t(8;21) was associated with a significantly higher myeloid differentiation and with a good response to chemotherapy. Moreover, among the patients with refractory anemia with excess of blasts in transformation (RAEB-T) the t(8;21) was also significantly associated with a higher myeloid differentiation and a good response to chemotherapy. M2 patients with t(8;21) could be distinguished on a number of hematological parameters, eg white blood cell count and percentage of bone marrow myeloblasts and promyelocytes, from RAEB-T carrying the t(8;21). Based on these findings we suggest that leukemia patients carrying t(8;21) can be grouped into two types; overt acute myeloid leukemia (M2) and smoldering or slowly evolving myeloid leukemia.

Adult T cell leukemia cell lines that originated from primary leukemic clones also had a defect of expression of CD3-T cell receptor complex.

Surface phenotypes and genotypes of six T cell lines established from four patients with adult T cell leukemia (ATL) were compared with those of fresh ATL cells. The surface antigen densities of CD3 and T cell receptor (TCR) complex examined by OKT3 and WT-31 mAbs on fresh ATL cells were low. But three IL-2-dependent cell lines, SKT-2, SKT-5, and ATL-17-2, established from three patients expressed a high density of CD3-TCR complex on their surfaces. On the contrary, three other cell lines (SKT-1A, SKT-1B, and MMT-2), established from two other patients, expressed a low density of CD3-TCR complex. Genotypic analysis of TCR beta chain (T beta) gene and integration sites of the proviral genome of human T cell lymphotropic virus type 1 demonstrated that SKT-1A, SKT-1B, and MMT-2 were derived from the original leukemic clones. These apparent associations between a defect of expression of CD3-TCR complex and identical genotypes of fresh and cultured cells suggest that the defect of expression of CD3-TCR complex may play a key role for development of ATL.

Genotypic analysis of lymph node cells from patients with phenotypically undetermined cell lymphoma.

Rearrangements of immunoglobulin (Ig) heavy chain (JH) and T cell receptor beta chain (T beta) genes of lymph node cells from 28 patients with malignant lymphoma were studied. Fourteen of 28 patients were diagnosed as undetermined cell lymphomas, since a marked predominance of cells expressing a single light chain of Ig or T cell associated antigens was not demonstrated by phenotypic analysis. Of these patients, JH gene rearrangements were observed in 8 patients, whereas T beta gene rearrangements were detected in 9 patients. Although bigenotypes were seen and cell lineage was not determined in three cases, these results indicate that demonstration of Ig and T beta gene rearrangements is a powerful tool to determine cell lineage and clonality of lymphoma cells that do not express definitive surface phenotypes. Interestingly, 12 of 14 lymphoma cells whose lineage had been determined by phenotypic analysis showed rearrangements of two alleles; however, only single allelic gene rearrangement was observed in 11 of 14 lymph node cells from phenotypically undetermined cell lymphoma.

Expression of AML1 and ETO Transcripts in hematopoietic cells.

Recently, two genes, AML1 and ETO have been isolated from the chromosomal breakpoint of t(8;21). In this study, we isolated and identified fusion transcripts from a leukemic cell line carrying t(8;21). We demonstrated by PCR analysis that these transcripts are consistently expressed in fresh leukemic cells with t(8;21). On the other hand, the wild type of ETO is expressed in several hematopoietic cells from different lineage, while the expression of AML1 was present in all hematopoietic cells investigated. These widespread expression suggests these molecules play an essential role in hematopoiesis.

p53 gene mutation and loss of heterozygosity are associated with increased risk of disease progression in adult T cell leukemia.

Although the prototype of adult T cell leukemia (ATL) is an aggressive T cell neoplasm, ATL manifests four major clinical subtypes, acute, lymphoma, chronic, and smoldering. We studied the relationship between p53 gene alteration and clinical features in 34 patients with ATL, 14 acute type, 15 chronic type, and five crisis type transformed from chronic type. Using a polymerase chain reaction/single strand conformation polymorphism (PCR/SSCP) assay, followed by nucleotide sequencing, we detected mutations of the p53 gene in six of the 14 acute type patients, two of the five crisis type, and one of the 15 chronic type patients. Gene dosage studies, using PCR amplification and Southern blotting, showed loss of heterozygosity (LOH) of the p53 gene in four of the 14 acute type patients, two of the five crisis type, and one of 14 chronic type patients examined. These observations indicated that the frequency of p53 gene alterations in the acute and crisis types of ATL was markedly higher than that in chronic type, suggesting that p53 gene alteration plays a role in the disease progression of ATL.

All-trans retinoic acid therapy in relapsed/refractory or newly diagnosed acute promyelocytic leukemia (APL) in Japan.

We have conducted four prospective multicenter studies for acute promyelocytic leukemia (APL) using oral 45 mg/m2 all-trans retinoic acid (ATRA) daily. The first three studies were for relapsed/refractory APL, and the fourth study for newly diagnosed APL. In the first study with ATRA alone, 18 (82%) of 22 evaluable patients achieved complete remission (CR). Initial peripheral leukemia cell counts were significantly less in the CR cases (p < 0.01); < 100/microliters in 17 of 18 CR cases, and > or = 200/microliters in all failure cases. In the second study, if initial leukemia cell counts were more than 200/microliters, chemotherapy with daunorubicin and behenoyl cytarabine was first given, and then ATRA was started. Of 42 evaluable patients, 36 (86%) achieved CR. In the third study, if initial leukemia cell counts were more than 200/microliters, chemotherapy was concomitantly given with ATRA, and if during the ATRA therapy leukemia cell counts became more than 1000/microliters, chemotherapy was added. Of 46 evaluable patients, 36 (78%) achieved CR. Patients achieving CR received standard consolidation and maintenance chemotherapy, and the 29-month predicted disease-free survival (DFS) rate is 72% for 41 cases achieving their first CR with ATRA, and 20% for 49 cases achieving their second CR with ATRA. In the fourth study for newly diagnosed APL, if leukocyte counts were more than 3000/microliters, chemotherapy was concomitantly given with ATRA, and if during the ATRA therapy leukemia cell counts became more than 1000/microliters, chemotherapy was added. Of 109 evaluable patients, 97 (89%) achieved CR, and the 19-month predicted event-free survival rate for all patients is 78%, and the DFS rate is 88% for 97 cases achieving CR. ATRA produces a high CR rate in both relapsed/refractory and newly diagnosed APL, and should be incorporated in the first-line therapy of this disease.

Gene rearrangements of T cell receptor beta and gamma chains in HTLV-I infected primary neoplastic T cells.

Rearrangements of T cell receptor beta and gamma chain (T beta and T gamma) genes were analyzed by Southern blot method in samples from 30 patients with adult T cell leukemia (ATL) and 17 patients with non-ATL T cell neoplasms. The DNA probes used were the constant and joining region of T beta gene and the joining region of T gamma gene. Rearranged bands of T beta gene on one or both allelic chromosomes were detected in all neoplastic T cells, even those of smoldering ATL, in which only a small percentage of peripheral blood T cells were detected as leukemic. T gamma gene was rearranged in the cells of all but one patient, the exception being one ATL patient. In order to test whether any given variable region (V) of T beta gene was expressed in ATL cells, two functionally rearranged V beta sequences of ATL were compared with a V beta sequence from T cells acute lymphoblastic leukemia cells. No significant homologies were noted among the three deduced gene product amino acid sequences, confirming that T beta molecules of ATL cells contained no specific structures in common. The observed heterogeneity of T beta and T gamma gene rearrangements in ATL cells further supported these findings.

CD4+ CD8+ granular lymphocytic leukemia arising in a patient with acute myeloblastic leukemia.

A 59-year-old woman who had an 8-year history of acute myeloblastic leukemia (AML) developed granular lymphocytic leukemia (GLL). She had a small number of granular lymphocytes (GL) in her bone marrow (BM) at the onset of AML. The GL increased during complete remission (CR) of AML, but not at the relapse. During the third CR state of AML, GL increased to 4.0 x 10(9)/l in the peripheral blood (PB). The GL were T-cell receptor (TCR) alpha beta+ T cells and expressed both CD4 and CD8 antigens. Rearrangements of TCR beta and gamma chain genes were detected in the peripheral blood mononuclear cells (PBMNC), confirming that this patient had GLL. The PBMNC from the patient responded weakly to PHA or ConA, yet they responded to her own bone marrow mononuclear cells (BMMNC) or CD4-depleted BMMNC that contained AML cells stronger than her own PBMNC or normal PBMNC. These observations suggest that monoclonal proliferation of GL developed after the reactive proliferation of GL in response to AML cells.

Acute unclassified leukemia originating from undifferentiated cells with the aberrant rearrangement and expression of immunoglobulin and T-cell receptor genes.

To analyze the development pathways of early hematopoietic cells, we studied the rearrangement and expression of the immunoglobulin (Ig) and T-cell receptor (TCR) genes in 12 patients with acute unclassified leukemia (AUL). Leukemia cells from these patients were negative for myeloperoxidase staining and failed to express B-cell, T-cell, or megakaryocyte associated antigens. The expression of the CD7 antigen, myeloid associated antigens, or both was detected in three patients each. Ig and/or TCR gene rearrangements were detected in seven of the 12 patients, and five had rearrangement of both the Ig and TCR genes. Full length mature TCR gene transcripts were not demonstrated in most of the patients showing TCR gene rearrangements. In contrast, cells from two patients with germline configurations of the Ig and TCR genes tested expressed truncated forms of both Ig and TCR genes. These results suggest that AUL may generally originate from undifferentiated cells with an aberrant rearrangement and/or expression of the Ig and TCR genes.

Dual mutations in the AML1 and FLT3 genes are associated with leukemogenesis in acute myeloblastic leukemia of the M0 subtype.

Point mutations of the transcription factor AML1 are associated with leukemogenesis in acute myeloblastic leukemia (AML). Internal tandem duplications (ITDs) in the juxtamembrane domain and mutations in the second tyrosine kinase domain of the Fms-like tyrosine kinase 3 (FLT3) gene represent the most frequent genetic alterations in AML. However, such mutations per se appear to be insufficient for leukemic transformation. To evaluate whether both AML1 and FLT3 mutations contribute to leukemogenesis, we analyzed mutations of these genes in AML M0 subtype in whom AML1 mutations were predominantly observed. Of 51 patients, eight showed a mutation in the Runt domain of the AML1 gene: one heterozygous missense mutation with normal function, five heterozygous frameshift mutations and two biallelic nonsense or frameshift mutations, resulting in haploinsufficiency or complete loss of the AML1 activities. On the other hand, a total of 10 of 49 patients examined had the FLT3 mutation. We detected the FLT3 mutation in five of eight (63%) patients with AML1 mutation, whereas five of 41 (12%) without AML1 mutation showed the FLT3 mutation (P=0.0055). These observations suggest that reduced AML1 activities predispose cells to the acquisition of the activating FLT3 mutation as a secondary event leading to full transformation in AML M0.