1. ¹Department of Pathology, Astrid Lindgren Child Hospital, Karolinska Institutet at Karolinska University Hospital, Stockholm, Sweden
2. ²Department of Hematology, Center for Molecular Medicine, Astrid Lindgren Child Hospital, Karolinska Institutet at Karolinska University Hospital, Stockholm, Sweden
3. ³Department of Immunology, Erasmus MC, Rotterdam, The Netherlands
4. ⁴Childhood Cancer Research Unit, Astrid Lindgren Child Hospital, Karolinska Institutet at Karolinska University Hospital, Stockholm, Sweden
5. ⁵Department of Epidemiology, Institute of Mother and Child Health, Warsaw, Poland

Correspondence: Msc M Malec, Department of Pathology, CCK R8:02, Karolinska Hospital, S-17176 Stockholm, Sweden. Fax: +46 851775843; E-mail: maria.malec-zacharski@cmm.ki.se

Received 6 February 2004; Accepted 17 June 2004; Published online 5 August 2004.

Abstract

Detection of minimal residual disease (MRD) in follow-up samples from patients with ALL is essential for evaluation of treatment response. We applied multicolor flow cytometry and real-time quantitative PCR (RQ-PCR) to compare MRD results in 71 follow-up samples from 22 children treated for ALL. When results obtained by flow cytometry and RQ-PCR were grouped into positive–negative categories, a significant level of agreement was found in 72% of samples (P<0.001). However, if a cutoff level of 0.01% was applied, the concordance was 89%. MRD could be quantified in 19 samples by both methods, showing a strong correlation (P<0.01). Nevertheless, MRD levels differed more than five-fold between both methods in 4/19 samples. In 20 (28%) samples, the two techniques showed discordant results. Most discordant results (17/20) were due to the limited sensitivity of flow cytometry analysis within the range 0.01–0.001%; remaining discordant results were due to the instable or subclonal IG/TCR gene rearrangements or a limited quantitative range of the applied RQ-PCR targets. Although concordant results could be obtained by flow cytometry and RQ-PCR analysis, MRD levels may differ. Therefore, MRD data obtained by these two techniques are not yet easily exchangeable.