EXPRESSION LEVELS OF WT1 AND NPM1 AND NOVEL NONSPECIFIC MARKERS AS TOOLS FOR EVALUATING MINIMAL RESIDUAL DISEASE IN AML

Background:

Monitoring of minimal residual disease (MRD) is an important tool in the medical management of acute myeloid leukemia (AML). Of the specific molecular markers, mutations of the nucleophosmin 1 (NPM1) gene represent the most frequent aberration. This makes NPM1 a favorite gene for MRD detection. Approximately one half of AML patients do not have a suitable specific molecular marker for MRD monitoring. Therefore, development of sensitive assays for quantification of nonspecific leukemia-associated antigens (LAA) should be focused on, along with the search for rare specific mutations. The Wilm's tumor gene (WT1) has been suggested as a possible molecular marker of MRD in AML as it is overexpressed in 80% of AML patients at diagnosis. The LAAs that we focused on were PRAME, MSLN, ST18, XAGE1, CSPG4, CA9 and BAALC in genes.

Aims:

To examine selected LAAs as potential tools for MRD monitoring in AML.

Methods:

Established IVD CE protocols of fluorescence-based quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and protocols based on TaqMan Gene Expression Assays^® were used for quantification of selected targets.

Results:

Of the 475 patients treated at the Institute of Hematology and Blood Transfusion in Prague in 2002-2012, 113 (23.8%) had a mutation in the NPM1 gene. Of the 45 patients with NPM1 mutation and follow-up >4 months, 7 never reached MRD negativity while sustaining hematological remission and 12 suffered hematological relapse. MRD positivity preceded hematological relapse by a median of 3.23 months.

Overexpression of WT1 in peripheral blood was detected in 199 of 211 patients (94.3%) at diagnosis. Thirty-three experienced relapse. Median time from MRD positivity to hematological relapse was 1.8 months.

MRD quantities monitored by NPM1 on mRNA level were compared to WT1 expression in 60 AML patients with a median follow-up of 12.3 months (range 1.32–110.4). Both methods for MRD detection correlated significantly (p<0.0001).

Levels of selected LAAs (MSLN, ST18, XAGE1, CSPG4, CA9) were evaluated in 153 AML patients at diagnosis. Overexpression of MSLN was demonstrated in 22.5%. However, the high expression of MSLN in normal peripheral blood makes this marker unsuitable for MRD monitoring. This is not the case of ST18, XAGE1, CSPG4 and CA9, which were overexpressed in 50.3%, 17.9%, 45.7% and 36.4% respectively. In 12 patients (7.8%) with high expression of a particular LAA at diagnosis, it was possible to trace MRD during the course of the disease. MRD data were in concordance with the disease status. Moreover, in seven of these patients, LAA was the only MRD marker because of the low expression of both WT1 and NPM1.

Levels of BAALC and PRAME were monitored in 373 AML patients at diagnosis. Overexpression of BAALC was demonstrated in 169 patients (45.3%). In 14 patients, MRD was monitored during the course of disease and, similarly, significant correlation of BAALC expression levels with those of WT1 has been found (p<0.0001). The high expression of PRAME was detected in 91 patients (24.4%) at diagnosis. In 5 patients, MRD was monitored during the course of disease. Its expression rose in concordance with PML/RARA transcripts while WT1 expression stayed below the upper normal limit.

Summary / Conclusion:

By combining methods for detecting NPM1 mutations and elevated LAA expression, a suitable MRD marker was found for every AML patient in our cohort. Median time from MRD positivity to hematological relapse was longer by 1.4 months in the NPM1 group compared to WT1.

Supported by IGA MZČR grant NS10632-3/2009 and grant IHBT00023736.

Keywords: AML, MRD, WT1

Abstrakta v časopise Haematologica 2013, Suppl1

Online Program