Clinical usefulness of WT1 mRNA expression in bone marrow detected by a new WT1 mRNA assay kit for monitoring acute myeloid leukemia: a comparison with expression of WT1 mRNA in peripheral blood.

We have previously shown the clinical usefulness of Wilms' tumor 1 gene (WT1) mRNA expression in peripheral blood (PB) as a minimal residual disease (MRD) monitoring marker in 191 acute myeloid leukemia (AML) patients using the WT1 mRNA assay kit "Otsuka" (Otsuka Pharmaceutical Co., Ltd.; "former kit"). In contrast, the usefulness of WT1 mRNA expression in bone marrow (BM) has been investigated in only a limited number of subjects using former kit. Following that previous study, a next-generation kit, WT1 mRNA assay kit II "Otsuka" (Otsuka Pharmaceutical Co., Ltd.; "new kit") has been newly developed. In the present study, we aimed to evaluate the performance of the new kit and to investigate the clinical usefulness of WT1 mRNA expression in BM. The PB and BM were collected on the same day from 164 blood disease patients, including 118 AML patients. WT1 mRNA expression was determined using the new and former kits and the values obtained were compared. The performance of new kit was shown to be equivalent to that of former kit. As reported in PB, WT1 mRNA expression in BM was found to be a useful marker for monitoring disease status as well as for a diagnosis of early stage relapse in AML patients.