Nordic CML Study Group Quality and Standardization Rounds for Quantitative RT-PCR of BCR-ABL To Facilitate Reporting on the International Scale.

Measuring the level of BCR-ABL transcripts by real-time quantitative polymerase chain reaction (RQ-PCR) has been shown to be a highly sensitive and specific method for evaluating residual disease burden in chronic myeloid leukemia (CML). In the IRIS trial, a 3-log reduction of BCR-ABL transcripts from a baseline median pre-treatment level was termed a “major molecular response”, and achieving this degree of minimal residual disease (MRD) was related to a more favorable prognosis. Recently it was proposed that the residual disease scale used in the IRIS trial should be named “International Scale” (IS) and this scale is recommended to be used in future studies of CML treatment. Since the baseline in the IRIS trial can no longer be reproduced, a project for distributing reference material has been initiated by the original IRIS study reference laboratory in Adelaide and by a secondary European reference laboratory in Mannheim. Within the framework of the Nordic CML Study Group, RQ-PCR for BCR-ABL is routinely performed in 13 clinical laboratories located in Finland, Sweden, Norway and Denmark. Only two Nordic laboratories had an opportunity to receive reference material from Mannheim. Therefore it was necessary to complement this effort by performing a Nordic quality and standardization round based not only on the external reference material but also on local pre-treatment samples from CML patients. Thus each of the participating laboratories prepared samples representing minimal residual disease and also additional pre-treatment CML samples. These samples were divided into 13 identical aliquots and distributed to all other participants this summer. By this approach we can not only check reproducibility of measurements, but also evaluate different laboratory specific steps in the procedures, such as the importance of source cell material, RNA isolation method, control genes, model of thermocycler and methods/enzymes used in reverse-transcription and RQ-PCR. Based on the results, provisional conversion factors for adjustment of the BCR-ABL transcript levels to the International Scale will be produced for all participating laboratories. This work is an example on successful international RQ-PCR standardization, which is essential for clinical and research estimation of MRD in CML patients.