The clinical significance of WT1 gene expression at diagnosis and during therapy of AML has not yet been resolved. We analysed WT1 expression at presentation in an unselected group of 47 childhood AML patients using real-time quantitative reverse-transcription PCR. We also showed that within the first 30 h following aspiration RQ-RT-PCR results were not influenced by transportation time. We observed lower levels of WT1 transcript in AML M5 (P = 0.0015); no association was found between expression levels and sex, initial leukocyte count and karyotype-based prognostic groups. There was significant correlation between very low WT1 expression at presentation and excellent outcome (EFS P = 0.0014). Combined analysis of WT1 levels, three-colour flow cytometry residual disease detection and the course of the disease in 222 samples from 28 children with AML showed remarkable correlation. Fourteen patients expressed high WT1 levels at presentation. In eight of them, who suffered relapse or did not reach complete remission, dynamics of WT1 levels clearly correlated with the disease status and residual disease by flow cytometry. We conclude that very low WT1 levels at presentation represent a good prognostic factor and that RQ-RT-PCR-based analysis of WT1 expression is a promising and rapid approach for monitoring of MRD in approximately half of paediatric AML patients.

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Wilms' tumor gene 1 (WT1) is overexpressed in the majority (70-90%) of acute leukemias and has been identified as an independent adverse prognostic factor, a convenient minimal residual disease (MRD) marker and potential therapeutic target in acute leukemia. We examined WT1 expression patterns in childhood acute lymphoblastic leukemia (ALL), where its clinical implication remains unclear. Using a real-time quantitative PCR designed according to Europe Against Cancer Program recommendations, we evaluated WT1 expression in 125 consecutively enrolled patients with childhood ALL (106 BCP-ALL, 19 T-ALL) and compared it with physiologic WT1 expression in normal and regenerating bone marrow (BM). In childhood B-cell precursor (BCP)-ALL, we detected a wide range of WT1 levels (5 logs) with a median WT1 expression close to that of normal BM. WT1 expression in childhood T-ALL was significantly higher than in BCP-ALL (Po0.001). Patients with MLL-AF4 translocation showed high WT1 overexpression (Po0.01) compared to patients with other or no chromosomal aberrations. Older children (X10 years) expressed higher WT1 levels than children under 10 years of age (Po0.001), while there was no difference in WT1 expression in patients with peripheral blood leukocyte count (WBC) X50 Â 10 9 /l and lower. Analysis of relapsed cases (14/125) indicated that an abnormal increase or decrease in WT1 expression was associated with a significantly increased risk of relapse (P ¼ 0.0006), and this prognostic impact of WT1 was independent of other main risk factors (P ¼ 0.0012). In summary, our study suggests that WT1 expression in childhood ALL is very variable and much lower than in AML or adult ALL. WT1, thus, will not be a useful marker for MRD detection in childhood ALL, however, it does represent a potential independent risk factor in childhood ALL. Interestingly, a proportion of childhood ALL patients express WT1 at levels below the normal physiological BM WT1 expression, and this reduced WT1 expression appears to be associated with a higher risk of relapse.

The presence of TEL/AML1 fusion gene in childhood acute lymphoblastic leukaemia (ALL) defines a subgroup of patients with better than average outcome. However, the prognostic significance of this aberration has recently been disputed by the Berlin-Frankfurt-Mü nster (BFM) study group due to its relatively high incidence found in relapsed patients (