Minimal residual disease detection in acute myeloid leukemia by mutant nucleophosmin (NPM1): comparison with WT1 gene expression.

BACKGROUND: Molecular analysis of minimal residual disease is only applicable in acute myeloblastic leukemia (AML) patients with genetic markers (20-30%). This study analyzes the feasibility of the real-time quantitative polymerase chain reaction (RQ-PCR) assay to detect mutant nucleophosmin (NPM1) during follow-up in AML patients. Moreover, we compare the NPM1 results with those of WT1 expression to MRD assessment. METHODS: The study includes 97 samples from 24 AML patients with type A NPM1 mutation at diagnosis. MRD was evaluated simultaneous by RQ-PCR assay to detect NPM1-mutated and WT1 expression. RESULTS: The expression levels of WT1 and NPM1 in 93 paired samples showed a strong positive correlation (r=0.81; p<0.0001). However, the kinetics of disappearance were different, WT1 decreased rapidly after induction but maintained these residual levels after treatment in patients in complete remission, whereas NPM1 experienced a mild reduction after induction but was undetectable in long survivor patients. CONCLUSIONS: This study shows the feasibility of the RQ-PCR assay to monitor MRD in AML patients carrying NPM1 mutations and its advantage over RQ-PCR assay for WT1. Owing to NPM1-mutated is specific of leukemic cells and shows higher levels at presentation.

High-level amplification of the RUNX1 gene in two cases of childhood acute lymphoblastic leukemia.

The RUNX1 (alias AML1) gene is involved in several patterns of chromosomal translocations and rearrangements associated with human acute leukemia. Often, multiple signals for AML1 have been observed in childhood acute lymphoblastic leukemia (ALL) due to frequent polysomy of chromosome 21 in this leukemia. Additionally, high-level amplification of AML1, in the absence of polysomy of chromosome 21, has been reported in childhood ALL. We report two new cases of childhood ALL, without a ETV6/RUNX1 (alias TEL/AML1) rearrangement, showing high-level amplification of the AML1 gene detected by fluorescence in situ hybridization and comparative genomic hybridization analysis. The first case was an 11-year-old girl with 7-12 signals for AML1 in nearly 84% of the cells, and the loss of a TEL allele. In the second patient, a 6-year-old girl, multiple copies of the AML1 gene were also observed in 99% of the cells, although no deletion of TEL was found. The similarity in the clinicobiologic features of all the cases with this abnormality points to an emerging molecular cytogenetic subgroup of B-cell precursor ALL and suggests a possible dosage effect of AML1 in the pathogenesis of leukemia.

A t(17;20)(q21;q12) masking a variant t(15;17)(q22;q21) in a patient with acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is genetically characterized by a reciprocal translocation between chromosomes 15 and 17, the t(15;17)(q22;q21), which results in the fusion gene PML/RARA. A small proportion of patients with APL have complex or simple variants of this translocation. We report the case of a 31-year-old woman with APL (FAB-M3 classical form) carrying an apparently balanced translocation t(17;20)(q21;q12) masking a t(15;17)(q22;q21) confirmed by fluorescence in situ hybridization (FISH) and molecular studies. The patient was treated with an all-trans-retinoic acid (ATRA) plus anthracycline-based protocol and achieved complete remission, with no recurrence to date. These results illustrate the usefulness of combining cytogenetics, FISH, and reverse transcription-polymerase chain reaction (RT-PCR) methods to evidence the PML/RARA fusion gene in cases with morphologic suspicion of APL with variant or cryptic t(15;17).