Cryptic splicing events in the iron transporter ABCB7 and other key target genes in SF3B1-mutant myelodysplastic syndromes.

The splicing factor SF3B1 is the most frequently mutated gene in myelodysplastic syndromes (MDS), and is strongly associated with the presence of ring sideroblasts (RS). We have performed a systematic analysis of cryptic splicing abnormalities from RNA sequencing data on hematopoietic stem cells (HSCs) of SF3B1-mutant MDS cases with RS. Aberrant splicing events in many downstream target genes were identified and cryptic 3' splice site usage was a frequent event in SF3B1-mutant MDS. The iron transporter ABCB7 is a well-recognized candidate gene showing marked downregulation in MDS with RS. Our analysis unveiled aberrant ABCB7 splicing, due to usage of an alternative 3' splice site in MDS patient samples, giving rise to a premature termination codon in the ABCB7 mRNA. Treatment of cultured SF3B1-mutant MDS erythroblasts and a CRISPR/Cas9-generated SF3B1-mutant cell line with the nonsense-mediated decay (NMD) inhibitor cycloheximide showed that the aberrantly spliced ABCB7 transcript is targeted by NMD. We describe cryptic splicing events in the HSCs of SF3B1-mutant MDS, and our data support a model in which NMD-induced downregulation of the iron exporter ABCB7 mRNA transcript resulting from aberrant splicing caused by mutant SF3B1 underlies the increased mitochondrial iron accumulation found in MDS patients with RS.

High-density single nucleotide polymorphism array analysis and ASXL1 gene mutation screening in chronic myeloid leukemia during disease progression.

We have undertaken a genome-wide single nucleotide polymorphism (SNP) array analysis of 41 chronic myeloid leukemia (CML) patients. In total, 44 regions of uniparental disomy (UPD) >3 Mb were identified in 24 of 32 patients in chronic phase (CP), and 21 regions of UPD >3 Mb were identified in 13 of 21 patients in blast crisis (BC). Chromosome 8 had the highest frequency of UPD regions in both CP and BC samples. Eight recurrent regions of UPD were observed among the 41 patients, with chromosome 8 showing the highest frequency. Ten regions of copy number change (CNC) >3 Mb were observed in 4 of 21 patients in BC, whereas none were observed in CP. We have identified several recurrent regions of UPD and CNC in CML that may be of pathogenetic importance. Overrepresentation of genomic aberrations (UPD and copy number gain) mapping to chromosome 8 was observed. Selected candidate genes mapping within the aberrant genomic regions were sequenced and mutation of the TP53 gene was observed in one case in BC and of the ASXL1 gene in 6 of 41 cases in CP or BC. Mutation of ASXL1 represents an important new molecular abnormality in CML.

hTERT, the catalytic component of telomerase, is downregulated in the haematopoietic stem cells of patients with chronic myeloid leukaemia.

Telomere shortening is associated with disease progression in chronic myeloid leukaemia (CML). To investigate the biology and regulation of telomerase in CML, we evaluated expression of the telomerase components, its regulators and several telomeric-associated proteins. Quantitative real-time-polymerase chain reaction (PCR) was used to compare gene expression in the CD34+/leukaemic blast cells of 22 CML patient samples to the CD34+ cell population of healthy individuals. hTERT, the catalytic component of telomerase, was downregulated in eight of 12 chronic phase (CP) patients (P = 0.0387). Furthermore, hTERT was significantly downregulated in two of three patients in accelerated phase (AP) and seven of seven patients in blast crisis (BC), P = 0.0017. Expression of hTR and telomeric-associated proteins TEP1, TRF1, TRF2, tankyrase and PinX1 was high in the majority of CP and AP patients. With the exceptions of TEP1 and hTR, expression of these factors was highest in CP and decreased during disease progression. Expression of c-Myc, a positive regulator of hTERT transcription, correlated with hTERT expression and decreased with disease progression, falling below control levels in BC. hTERT levels were increased in CP patients following successful treatment with imatinib, relative to untreated CP patients. We suggest that reduced hTERT expression directly causes the shortened telomeres observed in CML.

Application of the FICTION technique for the simultaneous detection of immunophenotype and chromosomal abnormalities in routinely fixed, paraffin wax embedded bone marrow trephines.

The use of interphase fluorescence in situ hybridisation (FISH) to study cytogenetic abnormalities in routinely fixed paraffin wax embedded tissue has become commonplace over the past decade. However, very few studies have applied FISH to routinely fixed bone marrow trephines (BMTs). This may be because of the acid based decalcification methods that are commonly used during the processing of BMTs, which may adversely affect the suitability of the sample for FISH analysis. For the first time, this report describes the simultaneous application of FISH and immunofluorescent staining (the FICTION technique) to formalin fixed, EDTA decalcified and paraffin wax embedded BMTs. This technique allows the direct correlation of genetic abnormalities to immunophenotype, and therefore will be particularly useful for the identification of genetic abnormalities in specific tumour cells present in BMTs. The application of this to routine clinical practice will assist diagnosis and the detection of minimal residual disease.

A pilot study of mitochondrial DNA point mutation A3243G in a sample of Croatian patients having type 2 diabetes mellitus associated with maternal inheritance.

In this work, patients having type 2 diabetes mellitus and diabetic mothers were tested for the presence of mitochondrial DNA point mutation A3243G. This mutation is associated with the MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes), diabetes and deafness. Twenty-two diabetic persons were screened. DNA was isolated from peripheral blood lymphocytes and from swabs of oral mucosa. The mitochondrial DNA point mutation A3243G was detected using PCR-RFLP test. The mutation was detected in oral mucosal DNA of two patients (but not from lymphocyte DNA). One patient was a man with hearing and visual impairments and proteinuria; the other was a woman having proteinuria but no hearing impairment. The mutation was not detectable in oral mucosal DNA from the control persons: 20 diabetic patients having diabetic fathers and 22 healthy, nondiabetic volunteers. The incidence of mitochondrial DNA point mutation A3243G in this study of Croatian diabetic patients is in line with data in the literature.

Prolegomenon for chronic lymphocytic leukaemia.

Chronic lymphocytic leukaemia (CLL) is a unique lymphoproliferative disorder that scarcely occurs under the age of 40; thereafter the incidence of CLL increases exponentially with age. CLL is characterized by progressive expansion of malignant CD5+ME+ B-cell clone accompanied by a myriad of cellular and humoral immune defects. Each of them might be linked to different clinically manifested complications such as increasing rate of infections, autoimmune disorders and disturbed immune surveillance against tumour cells. We assume that CLL occurs as a consequence of age-dependent, genetically related functional restrictions of the thymic microenvironment in supporting common lymphoid progenitor cells (CD5+ME+CD4-CD8-) to differentiate into mature T-cell and B-cell descendants. In conjunction with genetic abnormalities developing in B-cell progenitors, presumably expressing P glycoprotein (Pgp+), we postulate that developmentally altered T-cell descendants, along with quantitative imbalance among CD4+, their subsets and CD8+ lymphocytes in the peripheral blood, play an important additional role in facilitating the malignant B-cell clone emergence and in modulating the CLL clinical evolution. Namely, imbalance of any of T-cell-mediated cell interactive homeostatic mechanisms accompanied by imbalance in the production of various cytokines might in CLL influence leukaemic B-cell growth by deregulating inducer (c-myc and p53) and/or suppressor (bcl-2 and mutant p53) oncogenes responsible for the promotion or suppression of B-cell mitogenesis that may in turn further contribute to their impaired differentiation and/or differentiation arrest. In conclusion, CLL might be interpreted as a primary immunodeficiency syndrome developing in elderly population due to gradually evolving restriction of genetically controlled programs in the thymic microenvironment responsible for irregular maturation of common lymphoid progenitor cells that constitutively express CD5 antigen and ME receptor into T-cell and B-cell descendants.

Primary non-Hodgkin lymphoma of the humerus following traumatic injury: case report.

A case of primary non-Hodgkin lymphoma of the right humerus which occurred in a 21-year-old male patient after an impact to the right shoulder in a car accident in July 1983 is described. Seventeen years after the injury, due to a civil lawsuit, the biopsy material was revised. Immunohistochemical analysis showed CD20 and CD79a positivity on large pleomorphic cells, while small reactive lymphocytes were CD3, Bcl-2 and CD20 positive. Molecular analysis carried out with PCR revealed a monoclonal B-lymphocyte population. The diagnosis of diffuse large peripheral B cell lymphoma of the bone was confirmed. The present case concurs with the literature on primary bone lymphoma, in which the diagnostic problem, trauma-related presentation and an excellent prognosis of malignant tumour are emphasized.

Tyrosine phosphorylation in human lymphomas.

In a previous study, we showed that the high level of protein tyrosine phosphorylation present in lymphomas containing an anaplastic lymphoma kinase (ALK) can be demonstrated in routinely processed paraffin tissue sections using immunolabelling techniques. In the present study we investigated whether oncogenic tyrosine kinase activation also occurs in other categories of lymphoma by staining 145 cases of lymphoma covering those tumours with a range of different subtypes including those with morphological similarity to ALK-positive anaplastic large cell lymphoma (ALCL). Twelve cases of the borderline malignant disorder lymphomatoid papulosis were also studied. Twenty seven of the 28 cases of ALK-positive ALCL showed the extensive cytoplasmic labelling for phosphotyrosine in the neoplastic cells. The remaining case containing moesin-ALK exhibited membrane-associated phosphotyrosine expression. There was no nuclear phosphotyrosine labelling in any of the ALK-positive ALCL, even though ALK was present within the cell nuclei in 23 of the tumours. Variable degrees of phosphotyrosine labelling, usually membrane-restricted, were observed in 7/40 cases of ALK-negative ALCL, 9/29 cases of diffuse large B-cell lymphoma, 3/6 cases of mediastinal B-cell lymphoma, 2/7 cases of Hodgkin's lymphoma, 3/6 cases of peripheral T-cell lymphomas unspecified, 4/6 cases of B-cell chronic lymphocytic leukaemia, 2/6 cases of follicular lymphomas and 2/12 cases of lymphomatoid papulosis studied. However none of these phosphotyrosine-positive cases showed the strong cytoplasmic labelling comparable to that seen in ALK-positive lymphoma. We conclude that activation of a tyrosine kinase is probably not a major oncogenic event in lymphomas other than ALK-positive ALCL.

Clinical tumor cell distribution pattern is a prognostically relevant parameter in patients with B-cell chronic lymphocytic leukemia.

BACKGROUND AND OBJECTIVES: B-cell chronic lymphocytic leukemia (B-CLL) cells are variably distributed among the major lymphoid compartments contributing to the heterogeneous clinical presentation and course of this disease. In order to evaluate this variable distribution we propose a model for its clinical assessment. DESIGN AND METHODS: We introduce the model for tumor distribution (TD) assessment based on TTM scoring system, where TD value represents percentage of total tumor mass infiltrating peripheral blood and bone marrow (TD=TM(1)/TTM). TD in B-CLL can be categorized into 3 subgroups: pure leukemia if TD=100%, predominantly leukemia if TD=50-99% and predominantly lymphoma TD<50%. RESULTS: Among 341 B-CLL patients there were 22.6%, 55.1%, 22.3%, pure leukemia, predominantly leukemia and predominantly lymphoma cases, respectively. TD parameter was strongly associated in univariate analysis with TTM size, Rai and Binet stages, spleen size and beta(2) microglobulin. TD was associated with response to therapy and survival, with higher TD values translated into higher response rates and longer survival. However, in univariate and multivariate Cox analysis TD displayed much stronger relationship with prognosis in female patients, where it is the strongest independent predictor of survival along with age and Binet stage. INTERPRETATION AND CONCLUSIONS: TD, a quantitative and simple clinical parameter, easily assessed in all patients, offers a reliable tool for evaluation of tumor cell distribution in B-CLL. It has independent and strong prognostic power in females, as opposed to males, possibly unmasking important, yet unrecognized, biological difference in B-CLL patients.

Templated nucleotide addition and immunoglobulin JH-gene utilization in t(11;14) junctions: implications for the mechanism of translocation and the origin of mantle cell lymphoma.

The t(11;14)(q13;q32) between the BCL-1 and immunoglobulin heavy chain gene (IgH) loci in mantle cell lymphoma (MCL) are believed to be mediated by the mechanism of V(D)J recombination similar to the t(14; 18) in follicular lymphoma (FL). We have recently shown that the t(14;18) event creates staggered double-strand breaks in the BCL-2 locus, and that the t(14;18) junctions contain templated nucleotide insertions (T-nucleotides; U. Jäger et al., Blood, 95: 3520-3529, 2000). Reasoning that the earlier (pregerminal center) B-cell origin of MCL might be reflected in a different molecular structure of the chromosomal breakpoints, we PCR-amplified diagnostic samples from 93 patients. Thirty-six samples (39%) were positive for the direct (BCL-1/J(H)) and 23 for both direct and reciprocal (D(H)/BCL-1) junctions. The breaks on chromosome 14 exhibited features of V(D)J-mediated recombination as shown by D(H) and J(H) coding end processing. However, duplications of BCL-1 sequences in 39% of the 23 patients indicate staggered double-strand breaks in the major translocation cluster region (MTC). This is incompatible with V(D)J recombination and indicates a different mechanism of cleavage. The use of J(H)6 in the junctions (39%) was similar to that in the immunoglobulin genes of normal B cells and B-CLL, but considerably less than in FL. Only 2 of 36 samples contained a BCL-1/DJ(H) rearrangement, which was indicative of a previous DJ(H) rearrangement. Most importantly, 19% of the BCL-1/IgH junctions with inserts of > or =5 nucleotides contained error-prone copies (T-nucleotides) of 8-12 nucleotides originating from the surrounding BCL-1 or IgH regions, a lower rate than in FL. No correlation was found between the addition of T-nucleotides and the rate of somatic mutation in the immunoglobulin genes. We conclude that the t(11;14) and t(14;18) use the same basic mechanism of translocation including V(D)J-mediated recombination, double-strand staggered breaks, and template-dependent, error-prone DNA-synthesis. However, the distinct differences in the utilization of J(H) regions suggest that the t(11;14) occurs predominantly during an attempted primary D(H)-J(H) rearrangement in early B cells, whereas the t(14;18) mostly occurs during secondary rearrangement. This is in agreement with the pregerminal center B-cell origin of MCL.

The relevance of multidrug resistance-associated P-glycoprotein expression in the treatment response of B-cell chronic lymphocytic leukemia.

BACKGROUND AND OBJECTIVES: The aim of this study was to determine whether expression of P-glycoprotein (Pgp) is an intrinsic feature of B-lymphocytes in B-cell chronic lymphocytic leukemia (B-CLL) and how it correlates with hematologic indices and tumor load in the disease. Furthermore, the change of Pgp expression under cytotoxic treatment and its correlation to treatment outcome were studied. DESIGN AND METHODS: In 42 B-CLL patients, of whom 13 were sequentially monitored, expression of extracellular (MRK-16) and intracellular (C-219) Pgp epitopes on peripheral blood lymphocytes was determined by flow cytometry analysis and quantified by ratio of the mean fluorescence (RMF) in flow cytometry analysis. RESULTS: Median RMF values in B-CLL patients were higher than in age-matched controls. Pgp expression did not correlate with any of the hematologic features or clinical stage of the disease. Patients who received some type of cytoreductive treatment prior to the study had lower Pgp values for both measured epitopes (median RMF for C-219 and MRK-16 of 1.99 and 2.03 in comparison to those of non-treated patients: 3.11 and 2.88, respectively). In 13 patients monitored during treatment the decrease in RMF was noted after treatment with chlorambucil, with RMF values for both Pgp epitopes decreasing in responders. This was in contrast to unchanged or even increased RMF values in those patients who did not respond to therapy. INTERPRETATION AND CONCLUSIONS: Our study confirms the importance of quantitative evaluation of Pgp expression by flow cytometry. At the clinical level, cross-sectional, single test evaluation of Pgp is of limited value whereas sequential follow-up values correlate with treatment response.

Telomere length shortening is associated with disease evolution in chronic myelogenous leukemia.

We studied telomere length in the peripheral blood leukocyte samples of a large group of patients with chronic myelogenous leukemia (CML) by Southern blot hybridization using the (TTAGGG)4 probe. The average telomere length expressed as the peak telomere repeat array (TRA) of the peripheral blood samples obtained from a group of 34 healthy age-matched controls ranged between 7.6 and 10.0 kb and the mean peak TRA was 8.7 kb. Forty-one patients in the chronic phase of CML were studied; 32/41 (78%) showed telomere reduction (<7.6 kb) relative to age-matched controls and the mean peak TRA was 6.4 kb (range 4.0-10.6 kb). Serial samples were analysed from 12 patients at both chronic phase and during disease progression. The leukocyte DNA of all 12 patients in accelerated phase and/or blast crisis showed telomere reduction relative to age-matched controls and the mean peak TRA was 4.1 kb (range 3.0-5.4 kb). The peak TRA in the accelerated or blast phase was reduced compared with the corresponding paired sample in the chronic phase in all cases studied. These data show that a marked reduction in telomere length is associated with disease progression in CML.

Comparison of karyotype analysis and RT-PCR for AML1/ETO in 204 unselected patients with AML.

The chromosomal translocation t(8;21) (q22;q22) is often associated with acute myeloid leukemia with maturation (AML-M2) and can be detected by a reverse transcription-polymerase chain reaction (RT-PCR) for the AML1/ETO fusion mRNA. We investigated the prevalence of t(8;21) and AML1/ETO in 204 unselected patients with AML and compared the results of cytogenetic analysis with these of RT-PCR. Fifteen of 204 AML patients (7.4%) showed a t(8;21) in karyotype analysis. In 17 of 204 patients (8.3%) AML1/ETO was detected by RT-PCR. All patients who had a t(8;21) in conventional karyotyping also showed the gene rearrangement in molecular analysis, including one patient with a three-way translocation t(5;8;21). AML1/ETO was also detected in two AML patients lacking the t(8;21) cytogenetically. One had a normal diploid karyotype bone marrow (BM) at diagnosis; she has now been in CCR for 12 months. The second patient showed a complex chromosomal anomaly involving chromosome 21, but without a typical 8;21 translocation (BM in relapse). He died in relapse after an overall survival of 60 months. These data indicate that the results of karyotyping and RT-PCR are not completely identical, and molecular biology identifies approximately an additional 5-10% of AML1/ETO positive cases. The clinical relevance of our findings will have to be evaluated with larger patient numbers.

Reverse transcriptase-polymerase chain reaction (rt-PCR).

Reverse transcriptase polymerase chain reaction (RT-PCR) has become a well-established and powerful molecular technique for studying ribonucleic acids. It is used in medical diagnostics for detecting viral RNA, in hematology and oncology for detecting chimeric transcripts of rearranged genes (1), and in the broad area of research applications in gene expression studies. Since its introduction (2,3) the method is constantly finding new applications, especially in projects aimed at detecting and cloning differentially expressed genes (4,5).

Assessment of Prognostic Factors in 102 Patients with Myelodysplastic Syndrome-Osteoblasts are Related to Survival.

In a group of 102 patients with myelodysplastic syndrome an evaluation of bone marrow biopsy was performed in order to assess prognostic impact on survival. The following characteristics were included in the analysis: cellularity, erythropoiesis, granulopoiesis, thrombopoiesis, lymphatic nodules, mastocytes, dyserythropoiesis, dysgranulopoiesis, dysthrombopoiesis, blasts, atypical localisation of immature precursor cells, fibrosis, osteoblasts and osteoclasts on bone surfaces. Data were statistically analysed by stepwise Cox proportional hazards regression. Survival was compared between FAB sub-classes, with better prognosis for RA and RARS patients and poor for CMML patients. Better survival was found in patients without dysgranulopoiesis and in those with osteoblasts on bone surfaces. Agreement with established prognostic factors indicates a representative sample. Relationship of osteoblasts to better survival shows involvement of bone tissue in MDS, suggesting it might be useful to include assessment of bone tissue features in histopathologic evaluation.

Telomere length in myelodysplastic syndromes.

We have studied telomere length in the bone marrow cells or the granulocyte and lymphocyte cell fractions of 54 patients with myelodysplastic syndromes (MDS) by Southern blot hybridization using the (TTAGGG)4 probe. The average telomere length expressed as the peak telomere repeat array (TRA) in the peripheral blood, or bone marrow samples obtained from a group of 21 healthy age-matched controls (26-89 years old, mean age 55), ranged between 7.5 and 9.5 kb (mean peak TRA 8.6 kb). Twenty-four patients with refractory anemia (RA) were studied; 10/24 (42%) had telomere reduction (<7.5 kb) relative to age-matched controls and the mean peak TRA was 7.5 kb (range 4.0-9.0 kb). Eleven patients with RA with excess blasts (RAEB) were studied; 5/11 (45%) had reduced telomeres relative to age-matched controls and the mean peak TRA was 7.1 kb (range 5.0-9.0 kb). Eighteen patients with MDS in transformation to AML, comprising 15 with RAEB in transformation (RAEBt) and 3 with CMML in transformation (CMMLt), were also studied. Thirteen of eighteen patients (72%) had telomere reduction relative to age-matched controls and the mean peak TRA was 6.1 kb (range 3.5-9.0 kb). Thirty-six patients included in the study had either a normal karyotype or a simple karyotype (1 karyotypic change) and 20/36 (55%) of these had telomere reduction and the mean peak TRA was 7.1 kb (range 4.3-9.0 kb); 8 patients had a complex karyotype (3 or more karyotypic changes) and 5/8 (62%) of these had telomere reduction and the mean peak TRA was 6.1 kb (range 3.5-9.0 kb). We conclude, firstly that there is heterogeneity of telomere length in MDS and that this is observed throughout the spectrum of FAB-subtypes. Secondly, these data show that a marked reduction in telomere length in MDS if often associated with leukemic transformation and with the presence of complex karyotypic abnormalities.

High dose chlorambucil versus Binet's modified cyclophosphamide, doxorubicin, vincristine, and prednisone regimen in the treatment of patients with advanced B-cell chronic lymphocytic leukemia. Results of an international multicenter randomized trial. International Society for Chemo-Immunotherapy, Vienna.

BACKGROUND: In recent years, much attention has been paid to the possible efficacy of intensive chemotherapy in the treatment of advanced, progressive B-cell chronic lymphocytic leukemia (CLL) patients. For this reason, the International Society for Chemo-Immunotherapy, Chronic Lymphocytic Leukemia Cooperative Group, has begun a randomized multicenter trial comparing Binet's modified cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) regimen with continuous high dose chlorambucil (HD-CLB). METHODS: During the period January 1987 to May 1993, 228 previously untreated CLL patients from 7 cooperative institutions were randomized to this trial. Advanced and/or progressive disease was defined by high Total Tumor Mass (TTM) score (> 9), and/or short doubling time (DT) (< 12 months), and/or bone marrow failure. The response to therapy was defined by reduction of the initial TTM score. The end points of the trial were response rate, survival, and toxicity. RESULTS: HD-CLB resulted in a higher response rate than CHOP in evaluable cases, with 89.5% overall responses (complete response+partial response) versus 75%, respectively (P < 0.001). At the time of an analysis performed in July 1995 (after a median follow-up period of 37 months), overall survival was also longer in the HD-CLB treatment arm (median survival, 68 months) than in the CHOP treatment arm (median survival, 47 months) (P < 0.005). Toxicity was acceptable and comparable in the two treatment arms. CONCLUSIONS: The current study showed that HD-CLB is an effective and well-tolerated therapeutic option for patients with advanced and/or progressive CLL. Therefore, the authors recommend its wider use, possibly in comparison with and/ or in combination with new therapeutic agents, such as purine analogues.

Prognostic significance of WT1 gene expression at diagnosis in adult de novo acute myeloid leukemia.

We examined the presence of WT1-specific mRNA in bone marrow samples of 125 patients with de novo acute myeloid leukemia at diagnosis by two-step RT-PCR. The sensitivity of the assay was 1:100 (first step) and 1:10000 (second step), respectively. WT1-specific mRNA was detected in 73% of patients. No correlation was found between WT1 gene expression and age, FAB type, LDH and karyotype at diagnosis. All patients were treated with standard induction chemotherapy. There was no difference in the CR rate between WT1-positive and -negative patients. Using Kaplan and Meier plot analysis we found no difference in disease-free survival (DFS) and overall survival (OS) between patients displaying the WT1 transcript and WT1-negative patients. Furthermore, no significant interactions between WT1 PCR results and age, FAB type, LDH and karyotype on DFS and OS were demonstrable using Cox regression analysis. Eight patients who were WT1 PCR positive at diagnosis and achieved complete hematological remission following chemotherapy were monitored during the course of the disease. Based on our limited data demonstrating a heterogeneity of WT1 PCR results in CR we cannot draw any conclusions regarding the usefulness of WT1 PCR analysis for the early detection of relapse. We conclude that WT1 gene expression at diagnosis is not associated with specific characteristics of AML blast cells and is not a prognostic factor for CR, remission duration and overall survival in acute myeloid leukemia.