WT1 mRNA Expression in the Peripheral Blood of Patients with MDS Yields Additional Prognostic Information within the IPSS-R Risk Categories "Very Low", "Low" and "Intermediate"

Introduction:

The revised version of the International Prognostic Scoring System, (IPSS-R), is an accepted standard for assessing the prognosis of patients with MDS. Its usefulness may be further improved by integrating molecular findings. However, such efforts are impeded by limited access to molecular diagnostics, lack of standardized methodology, and a relatively low frequency of individual gene mutations in MDS. The Wilms' Tumor-1 (WT1) gene is overexpressed on mRNA level in the peripheral blood (PB) in about 50% of patients with MDS. The aim of this analysis was to determine whether PB WT1 expression status yields additional prognostic information.

Methods:

For this purpose, PB WT1 mRNA expression was measured in 91 newly diagnosed patients with MDS (WHO: MDS del5q, n=7; RARS, n=1; RCUD, n=4; RCMD, n=37; RAEB-I, n=16; RAEB-II, n=23; MDS/MPN unclassifiable, n=3 / IPSS-R: very low risk, n=3; low risk, n=28; intermediate risk, n=27; high risk, n=13; very high risk, n=20), using the Ipsogen® WT1 ProfileQuant® Kit. This standardized, commercially available assay uses a validated cut-off level of 50 WT1 copies/10⁴ABL copies for discrimination between normal and overexpression of WT1 in PB. MDS patients in our study cohort were stratified accordingly (normal WT1 expression with <50 WT1 copies versus overexpression with >50 WT1 copies). WT1 expression status was correlated with clinical parameters and outcome.

Results:

Overall, 53 MDS patients (58%) showed WT1 overexpression, which correlated significantly with WHO 2008 disease category and IPSS-R risk groups, as indicated by both the absolute WT1 levels (correlation with WHO 2008 type, p=0.0028, and IPSS-R, p=0.0075) and the frequency of WT1-overexpressing patients within the respective MDS subgroup (correlation with WHO 2008 type, p=0.0029, and IPSS-R, p=0.0027). Regarding the entire cohort, patients with elevated WT1 expression had a significantly lower progression-free survival (PFS) and overall survival (OS) compared to those with normal WT1 expression (p<0.0001 and p=0.0306). Furthermore, within the IPSS-R risk groups 'very low', 'low' and 'intermediate', PFS differed significantly between patients showing normal vs. elevated WT1 expression status (IPSS-R very low/low: median PFS 30.1 months vs. not reached, for WT1 high vs normal, respectively, p=0.0127; IPSS-R intermediate: median PFS 14.4 months vs. 59.5 months, for WT1 high vs. normal, respectively p=0.0240). These differences in PFS retained their prognostic significance in multivariate analysis after adjusting for IPSS-R (HR 0.306; 95% CI 0,156-0,598, p=0.001). However, they did not translate into a difference in overall survival, which was probably due to a relevant number of patients proceeding to allogeneic stem cell transplantation. Given the large proportion of patients displaying WT1 overexpression in the IPSS-R high and very high risk groups, it was not surprising that no significant prognostic subdivision by WT1 expression level was seen in these risk categories.

Conclusion:

Our results show that PB WT1 expression offers additional prognostic information in patients belonging to the IPSS-R risk groups 'very low', 'low' and 'intermediate'. Assessment of WT1 expression status at diagnosis is a relatively time and cost efficient method that can be performed without patient discomfort and may help to identify MDS IPSS-R low and intermediate patients at risk for early progression.