The Presence Of Residual Disease After Induction and/Or Consolidation Therapy Based On Wilms’ Tumor 1 (WT1) Expression Is a Strong Prognostic Factor For Relapse and Survival In AML

The Wilms' tumor 1 (WT1) gene, located on chromosome 11p13, encodes a transcription factor with both oncogene and tumor suppressor functions. WT1 is reportedly overexpressed in 90% of patients with acute myeloid leukemia (AML) and thus can be used for minimal residual disease (MRD) monitoring by quantitative RT-PCR. The aim of the present study was to analyze the usefulness of WT1 as a marker for MRD in AML after chemotherapy and as a predictor of relapse and survival.

This retrospective and multicentric study included 114 patients with WT1-overexpressed AML (Table 1). Quantitative assessment of WT1 transcript levels was performed by quantitative RT-PCR in 283 bone marrow (BM) samples at diagnosis, post-induction and post-consolidation. WT1 gene expression was calculated by relative quantification using the normalized ratio of the target gene (WT1) related to a reference gene (GUS) and using cell line K562 as calibrator. Inter-laboratories methodological standardization was accomplished through a pilot study with 10 BM donor samples, 20 BM patient samples and commercial WT1 plasmids (ProfileQuant Kit, Ipsogen-Qiagen).

No significant differences in WT1 gene expression (cycle threshold, Ct) were observed between different laboratories in the pilot study. The cut-off value of WT1 over-expression in BM was established in 0.55% (median+2SD values from healthy donors). Median WT1 expression in patient samples at diagnosis was 29.5% (range, 2-1220). Differential expression at diagnosis was not correlated with age, sex, leukocytes, karyotype (risk), however a higher expression in patients with AML-M1 and AML-M2 subtypes as well as patients with mutant NPM1 and/or ITD-FLT3 was observed. Most patients (88.6%; 101/114) received intensive chemotherapy as induction treatment. After induction, 80.2% (81/101) of patients had available WT1 data, of which 23.45% (19/81) were positive. In addition, 79.8% (91/114) received intensive treatment during consolidation. WT1 results were available for 75.5% (66/91), of which 22.7% (15/66) were positive. Post-induction WT1 positivity was correlated with a higher cumulative incidence of relapse (CIR; 2 years 76% vs. 28.2% p=0.002) and a lower overall survival (OS; 2 years, 44.9% vs. 78.2% p=0.022; Figure 1a,b). Similar results were obtained when patients intensified with allogeneic stem cell transplantation (allo-SCT) were excluded from the analysis: higher CIR (2 years 88.9% vs. 32.5%; p=0.005) and lower OS (40% vs. 76.2% p=0.17). Post-consolidation WT1 positivity was correlated with a trend to a higher CIR (2 years 60.3% vs. 41.4% p=0.21) and a lower OS (2 years 44.9% vs. 66% p=0.09; Figure 1c,d). Statistically significant results were obtained after consolidation when patients treated with allo-SCT were excluded from the analysis: higher CIR (2 years 100% vs. 40.1% p=0.005) and lower OS (2 years 20% vs. 66% p=0.003).

WT1 is a useful marker for MRD in AML patients undergoing chemotherapy (induction and consolidation) which allows anticipation of relapse and survival. Post-induction results were a strong risk factor of relapse and survival in all patients, including those intensified with allo-SCT. By contrast post-consolidation results are especially relevant in the group of patients not treated with allo-SCT. Intensification with allo-SCT overcomes the poor prognosis derived from positive post-consolidation WT1 results.

Paper presented on behalf of the Hematological Molecular Biology Group (GBMH) of the Spanish Society of Hematology (SEHH).

No relevant conflicts of interest to declare.