Latham, S.Bartley, P.Budgen, B.Ross, D.Hughes, E.Branford, S.White, D.Hughes, T.Morley, A.2017-06-182017-06-182016Journal of Clinical Pathology, 2016; 69(9):817-8210021-97461472-4146http://hdl.handle.net/2440/106037RT-qPCR is used to quantify minimal residual disease (MRD) in chronic myeloid leukaemia (CML) in order to make decisions on treatment, but its results depend on the level of BCR-ABL1 expression as well as leukaemic cell number. The aims of the study were to quantify inter-individual differences in expression level, to determine the relationship between expression level and response to treatment, and to investigate the effect of expression level on interpretation of the RT-qPCR result.BCR-ABL1 expression was studied in 248 samples from 65 patients with CML by determining the difference between MRD quantified by RT-qPCR and DNA-qPCR. The results were analysed statistically and by simple indicative modelling.Inter-individual levels of expression approximated a normal distribution with an SD of 0.36 log. Expression at diagnosis correlated with expression during treatment. Response to treatment, as measured by the number of leukaemic cells after 3, 6 or 12 months of treatment, was not related to the level of expression. Indicative modelling suggested that interpretation of RT-qPCR results in relation to treatment guidelines could be affected by variation in expression when MRD was around 10% at 3 months and by both expression variation and Poisson variation when MRD was around or below the limit of detection of RT-qPCR.Variation between individuals in expression of BCR-ABL1 can materially affect interpretation of the RT-qPCR when this test is used to make decisions on treatment.en© 2016, BMJ Publishing Group Ltd and the Association of Clinical PathologistsNeoplasm, ResidualJournal article003004336710.1136/jclinpath-2015-2035380003843237000132-s2.0-84958093178236066Ross, D. [0000-0001-7171-2935]Branford, S. [0000-0002-1964-3626] [0000-0002-5095-7981]White, D. [0000-0003-4844-333X]Hughes, T. [0000-0002-0910-3730] [0000-0002-7990-4509]