WT1 Overexpression after Induction Therapy in Children AML Is Associated with Higher Risk of Relapse.

The Wilms’ s tumor gene (WT1) is a tumor suppressor gene highly expressed in most acute leukemias. To determine whether WT1 gene expression is a valuable and informative marker for minimal residual disease in pediatric AML, we quantified WT1 transcript amount by RQ-PCR in 92 de novo AML and 20 normal controls. The WT1 transcripts obtained were normalized with respect to the number of TBP transcripts and expressed as WT1 copy numbers by the ratio WT1/TBPx1000. The WT1 levels were extremely low in normal controls, and the median number of WT1 copies was 10 (range 4–30 ). A level above 50 copies was considered as significant. All the patients (aged 2 months-18 years, median age:5.9 years, male/female ratio 0.87) were treated for de novo AML between 1995 and 2003 in two French institutions and enrolled in LAM91, LAM01 and APLs French collaborative protocols. According to the FAB classification the repartition was: MO 5.4%, M1 4.3%, M2 18.5%, M3 14.1%, M4 and M4Eo 12%, M5 33.6 %, M7 10.9% and unclassified 1%. Cytogenetics features according to the MRC classification were favourable, intermediate or poor in 27% (23/83), 59% (49/83) and 13% (11/83) respectively. With a median follow up of 24 months (range 8–97months) OS was 75± 8% and EFS 60 ± 6%. At diagnosis WT1 overexpression was detected in 78.3% (72/92) with a median copy number of 2231 (range 50-429200). The WT1 values were significantly higher (p=0.02) in M2-FAB subtype and lower (p=0.01) in M5-FAB subtype while no correlation was found with WBC count or cytogenetic abnormalities. WT1 quantification for MRD was evaluable in 41/72 pts and positive in 9/32 at D40-50, 5/25 at M3-M5, 5/7at M6-M8. At least one analysis above 50 copies after induction therapy is associated with a significant risk of subsequent relapse 8/11 vs 8/30 ( p=0.007 ) RR=22 (IC 95%:46–118) and death 10/14 vs 3/30 ( p=0.001 ) RR=7.3 (IC95%: 1–34). Although retrospective analysis may include bias, we conclude that WT1 is a useful and informative molecular marker for MRD in pediatric AML and performed as prospective analysis in ELAM02 protocol.