Characterisation and Prognostic Significance of WT-1 Gene Expression in Acute Myeloid Leukemia (AML).

Background: Wilms’ tumour gene 1 (WT-1) is frequently over-expressed in adult AML and may be of prognostic value. We examined the prognostic utility of WT-1 expression in the peripheral blood, measured by RQ-PCR on diagnostic specimens, and characterised this compared to other clinical and biological predictors of survival.

Methods: RQ-PCR was performed in triplicate on samples from newly diagnosed AML patients, using the Corbett Rotorgene 3000. Values were averaged and levels expressed relative to 10⁴ ABL copies. Multivariate stratified Cox regression, with the stratification variable cytogenetic risk group and WT-1 levels analysed as a continuous variable, was used to model the outcomes of overall survival (OS) and event free survival (EFS).

Results: Samples were collected from 58 patients with AML. The median age was 66 years (range 16–82) and 30 were male. Seven had antecedent haematological disorders and 9 had received prior chemo/radiotherapy. Induction therapy was with cytarabine based regimens in 18, high dose cytarabine regimens in 20, ATRA/chemotherapy in 6 and supportive care in 14. Complete remission was achieved in 64% with 18% induction mortality. Median OS was 4 months (17 months in responders) and 27% at 2 years. The median WT-1 transcript level in diagnostic AML samples was 5122 (range 9–36125), while in normal control samples it was 3 (n=11, mean 3.6, SD 1.6).

In multivariate Cox regression, stratified by cytogenetic risk group, age (p<0.001), LDH (p<0.001) and performance status (p=0.04) retained prognostic significance for OS and EFS. Elevated peripheral blood WT1 levels were significantly associated with impaired OS (HR 1.24 per log₁₀ transcript levels p=0.022) and EFS (HR 1.31 per log₁₀ transcript levels p=0.0019). WT1 levels correlated with cytogenetic risk group (p=0.002 with higher levels seen in the favourable risk group), antecedent haematological disorder (p=0.05), peripheral blood blast percentage (p=0.05) and bone marrow blast percentage (p=0.01). WT1 levels were significantly higher in acute promyelocytic leukaemia (p=0.0001) compared to other AML subtypes. WT1 levels did not correlate with age (p=0.16), sex (p=0.12), prior chemo/radiotherapy (p=0.96), performance status (p=0.33) or LDH (p=0.91).

Conclusions: WT1 RQ-PCR levels are frequently elevated in peripheral blood from patients with AML at diagnosis and are associated with subtype, cytogenetic risk group, blast percentage and antecedent haematological disorder. Within specified cytogenetic risk groups, elevated WT1 levels may predict AML patients at high risk of relapse and subsequent mortality.