Stratification of Intermediate-Risk Acute Myeloid Leukemia According to the Expression Level of WT1 mRNA at Diagnosis
Authors: Fuse Kyoko , Akane Kaihatsu , Kitajima Toshiki , Momoi Akihito , Kasami Takuya , Katagiri Takayuki , Shibasaki Yasuhiko , Furukawa Tatsuo , Narita Miwako , Sone Hirohito , Masuko Masayoshi 
Published: November 2021

Abstract
Introduction
Despite advances in the genetic analysis of acute myeloid leukemia (AML), Wilms' tumor oncogene 1 (WT1) mRNA remains an important pan-marker of AML. A log reduction in WT1 mRNA expression after chemotherapy is a predictor of prognosis, and WT1 mRNA can be used as a marker of minimal residual disease or relapse. In the 1990s, a high expression level of WT1 mRNA at diagnosis was considered a poor prognostic factor. However, recent analyses have found that WT1 mRNA expression varies with AML type. Since the prognosis is affected by cytogenetic abnormalities and therapeutic intensity, we re-evaluated the clinical significance of WT1 mRNA expression at diagnosis in the context of the European Leukemia Net (ELN) risk classification and treatment.
Method
We retrospectively analyzed 216 patients at five institutions between 2011 and 2020. The expression level of WT1 mRNA was measured for all patients at diagnosis using bone marrow (BM) samples from 191 patients and peripheral blood (PB) samples from 25. WT-1 mRNA expression was measured using real-time quantitative polymerase chain reaction and the measured values were converted in normal logarithm. The median age at diagnosis was 62 (range: 23-93) years. The cytogenetic risk of ELN was classified as favorable (n = 41), intermediate (n = 123), and adverse risk (n = 41). Selected therapeutics were standard chemotherapy (n = 182, 84.3%, including CAG regimen; cytarabine, aclarubicin and G-CSF), hypomethylating agents or low-dose cytarabine (n = 19, 8.8%), and best supportive care (n = 15, 6.9%). Also, 143 patients (66.2%) received one or more courses of standard consolidation chemotherapy and 61 (28.3%) underwent allogeneic hematopoietic stem cell transplantation (allo-HCT). The median observation period was 518 [1-3418] days (Table 1). The overall survival (OS) and event-free survival (EFS) rates were assessed. Relapse or death was defined as an event, and OS was evaluated on the date of death.
Result
The median expression level of WT1 mRNA was 4.68 (range: 1.0-5.72) [log copies/µg RNA, units are omitted thereafter] in BM and 3.66 (range: 1.34-5.20) in PB (Table 1). Favorable-risk AML had the highest WT1 mRNA expression level in BM (4.95, p = 0.0054), whereas there was no difference between the expression levels in intermediate- and adverse-risk AML in BM (4.63 and 4.47, p = 0.711, Fig. 1A). WT1 mRNA expression in PB were 4.04, 3.84, and 3.05 for favorable-, intermediate-, and adverse-risk AML, respectively, and were higher for those with a favorable-risk AML (vs. adverse risk, p = 0.048, Fig. 1B). When WT1 mRNA expression level in BM was compared between the two groups, i.e., &lt;4.0 (BM-WT1 low) vs. ≥4.0 (BM-WT1 high), 2-year EFS rates were 26.8% and 49.7% (p = 0.0035) and 2-year OS rates were 44.9% and 61.5% (p = 0.00053), respectively. When WT1 mRNA expression level in PB was compared between the two groups, i.e., &lt;3.0 (PB-WT1 low) vs. ≥3.0 (PB-WT1 high), 2-year EFS rates were 0% and 51.5% (p = 0.023) and 2-year OS rates were 0% and 73.1% (p = 0.01), respectively. PB- or BM-WT1 low showed a worse prognosis at diagnosis.
Since AML prognosis is affected by ELN risk and selected therapeutics, we evaluated 109 intermediate-risk patients who had received at least one course of standard chemotherapy. Fifty of them (45.9%) underwent subsequent allo-HCT. The 2-year EFS rates of PB or BM-WT1 low (n = 25, PB = 2 and BM = 23) vs. PB or BM-WT1 high (n = 84, PB = 23 and BM = 61) were 23.9% and 50.4%, respectively (p = 0.023, Fig. 2A) and the 2-year OS rates were 51.2% and 64.6%, respectively (p = 0.03, Fig. 2B). PB or BM-WT1 low of intermediate-risk AML had a poor prognosis even with standard chemotherapy. Multivariate analysis adjusted for ages, the reduction rate of WT1 mRNA after induction chemotherapy, duration of receiving consolidation chemotherapy, allo-HCT, and PB or BM-WT1 low at diagnosis were independent poor prognosis factors for EFS in intermediate-risk AML (HR: 3.32, 95%CI: 1.29-8.53, p = 0.013). The OS rate of PB or BM-WT1 low also worsened (HR: 2.33, 95%CI: 0.88-6.18, p = 0.089) (Table 2). Whereas, the outcome of adverse-risk AML was not affected by PB or BM-WT1 low/high.
Conclusion
The expression level of WT1 mRNA at diagnosis was negatively correlated with prognosis. Favorable-risk AML had higher expressions of WT1 mRNA. PB or BM-WT1 low in intermediate-risk AML was associated with a poor prognosis. In standard-risk AML, WT1 mRNA may be a useful pan-marker to predict prognosis at diagnosis.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.