Prevalence and Prognostic Implications of WT1 Mutations in Pediatric AML Â: Report from Children’s Oncology Group

Molecular alterations of the WT1 gene have been associated with clinical outcome in adult AML. We evaluated the prevalence and prognostic significance of WT1 mutations in a cohort of 842 pediatric patients treated on pediatric AML trials CCG-2941, CCG-2961, or COG-AAML03P1. Exons 6–10 of the WT1 gene were evaluated by microcapillary electrophoresis and direct sequencing. Of the 842 samples diagnostic specimens analyzed, 68 (8%) contained mutations in exon 7 (n=62), exon 8 (n= 5), or exon 9 (n=1). Correlation analyses were done to determine whether the presence of WT1 mutations is associated with laboratory and disease characteristics and clinical outcome.

There were no differences in sex, race, median diagnostic blast %, or median diagnostic WBC count between samples from patients carrying WT1 mutations and those from patients who did not; however, such mutations were less common in the younger patients (age, 0–2 years; p<0.001) and in those with FAB M5 AML (p=0.009). Our evaluation of clinical outcome showed that the rate of complete remission after the first round of induction chemotherapy for those with and without WT1 mutations 74% and 80%, respectively (P=0.3) Actuarial overall survival (OS) from the time of study entry for patients with WT1 mutations was 35% vs. 52% for those without WT1 mutations; p=0.014. Corresponding event-free survival (EFS) was also significantly worse for those with WT1 mutations (27% vs. 41%; p=0.013).

We also evaluated associations between WT1 mutations and cytogenetic and molecular alterations. In the patients with WT1 mutations, 31% had inv(16) or t(8;21). There was also substantial overlap between WT1 mutation and FLT3/ITD, i.e., 29% of those carrying a WT1 mutation were FLT3/ITD- positive, whereas only 7% of patients without WT1 were FLT3/ITD-positive (p<0.001). In addition, 11q23 alterations were rare in patients with WT1 mutations (4% vs. 24%; p=0.002). Prognostic significance of WT1 mutations in FLT3/ITD-negative patients was determined. In a comparison of samples from FLT3/ITD-negative patients with WT1 mutations and those from patients who did not carry the 2 mutations, the OS (51% vs. 54%, respectively; p=0.5) and the corresponding EFS (34% and 43%, respectively; p=0.22) were not significantly different. The prognostic significance of the WT1 mutation was also determined in patients with a normal karyotype who were FLT3/ITD-negative. No significant differences were found in the OS (40% and 55%, respectively; p=0.23) or in the corresponding EFS values (31% and 45%, respectively; p=0.335). We conclude that about 8% of children with AML carry WT1 mutations, including novel mutations identified in exon 8. These mutations are associated with other cytogenetic and molecular alterations, and despite their overall association with poor outcome, the prognostic significance of WT1 mutations is less pronounced once the data are corrected for FLT3/ITD and cytogenetic abnormalities.