Log Reduction Levels of WT1 mRNA Expression in BM after Chemotherapies Are Predictive Markers of Good Prognosis in AML Patients Achieved CR after Induction Therapy

Introduction

While some prognostic factors such as chromosome or gene mutations in acute myeloid leukemia (AML) have been reported, the indication of allogeneic stem cell transplantation in first complete remission (CR) of AML patients is still controversial. Evaluation of minimal residual disease (MRD) during chemotherapy is considered as one of the predictive markers for the prognosis of AML patients. Detection of leukemia-specific chimeric genes by real-time quantitative polymerase chain reaction is the most sensitive method to quantify MRD. However, because over 50% of AML patients lack suitable leukemia-specific chimeric genes for the detection of MRD, other gene markers for assessing MRD are necessary for a greater proportion of AML patients. Wilms tumor gene 1 (WT1) mRNA transcript levels in peripheral blood have been reported as a suitable molecular marker of MRD for the prediction of relapse in most AML patients. In contrast, in acute lymphoblastic leukemia (ALL) patients, it remains to be elucidated whether early and/or deep reduction of tumor burden predicts a good prognosis in AML patients achieved CR.

Aims

In this study, we focused on the clinical relevance of the log reduction levels of WT1 mRNA transcript in bone marrow (BM) as MRD during chemotherapies, and also the association between WT1 mRNA transcript levels and outcomes in adult AML patients achieved CR.

Patients and methods

From 2007 to 2011, 48 AML patients who received chemotherapy at hospitals in our study group were enrolled in this study. Written informed consent was obtained from each patient before starting induction chemotherapy. We analyzed transcript levels of WT1 mRNA in BM at diagnosis, after induction therapy and after final consolidation therapy. WT1 mRNA levels were determined using the WT1 mRNA Assay Kit (Otsuka Pharmaceutical Co., Ltd., Tokyo, Japan) and normalized with GAPGH.

Result

We analyzed the expression levels of WT1 mRNA in 48 patients at diagnosis. Quantification of WT1 mRNA expression in BM at diagnosis was associated with neither disease-free survival (DFS) nor overall survival (OS). Twenty-eight of 32 patients who achieved CR could be analyzed for the expression levels of WT1 mRNA in BM after induction therapy. Expression levels of WT1 mRNA in BM after induction therapy were not associated with DFS and OS. Log reduction levels of WT1 mRNA transcript in BM after induction therapy were associated with DFS (P=0.0066) and OS (P=0.0074). Twenty-three CR patients could be examined for the expression levels of WT1 mRNA in BM after final consolidation therapy. Expression levels of WT1 mRNA in BM after final consolidation therapy were not associated with DFS and OS. Log reduction levels of WT1 mRNA transcript in BM after final consolidation therapy were associated with DFS (P=0.015) and OS (P=0.012). We analyzed the effect of log scales of WT1 mRNA expression levels in BM at diagnosis and the impact of log reduction levels of WT1 expression in BM by multivariate analysis adjusting stepwise p-values. Factors were adjustment for age, sex, SCT in 1CR and chromosome. The log scales of WT1 mRNA expression levels in BM at diagnosis were not associated with DFS and OS. We used Wd/i_log and Wd/c_log to assess the value of reduction of tumor burden. Wd/i_log was defined as a log scale of WT1 mRNA transcript level in BM at diagnosis divided by that after induction therapy. Wd/c_log was defined as a log scale of WT1 mRNA transcript level in BM at diagnosis divided by that after final consolidation therapy. Wd/i_log and sex were associated with DFS and only Wd/i_log was associated with OS. Hazard ratios of Wd/i_log for DFS and OS were 0.37 (P=0.0031) and 0.34 (P=0.0035), respectively, by every shallow remission level in log scale. Wd/c_log was also associated with DFS and OS. Hazard ratios for DFS and OS were 0.48 (P=0.0012) and 0.41 (P=0.022), respectively, by every shallow remission level in log scale.

Conclusion

Log reduction levels of WT1 mRNA expression in BM after induction therapy are suitable predictive markers for DFS and OS in AML patients achieved CR. It is suggested that early treatment response is important for AML patients such as ALL patients. Furthermore, log reduction levels of WT1 mRNA expression in BM after final consolidation therapy may be a predictive marker of good prognosis in AML and may be useful for the decision to proceed with allogeneic stem cell transplantation.