Monitoring chronic myeloid leukaemia therapy by real-time quantitative PCRin blood is a reliable alternative to bone marrow cytogenetics

We have developed a rapid real-time quantitative PCR method for measuring B CR-ABL mRNA levels in peripheral blood in chronic myeloid leukaemia (CML). The technique was used to monitor minimal residual disease for the early de tection of relapse and as an assessment of treatment response. Normal BCR m RNA was quantitated to control for RNA degradation and the results reported as a percentage of BCR-ABL/BCR. Every patient measured at diagnosis (n=21) had increased expression of BCR-ABL of up to 5-fold above the normal BCR l evels, With effective treatment the BCR-ABL levels decreased, The molecular data was correlated with Philadelphia chromosome levels in bone marrow and a good correlation was found when treatment induced a cytogenetic response (Spearman correlation = 0.94, P<0.0001, n = 67 samples). In patients recei ving interferon-alpha therapy we found a significant difference in the BCR- ABL levels between cytogenetic response groups. The method was sensitive, r eproducible, and readily detected a change in BCR-ABL transcript levels in serial blood samples, Sample throughput was high because post PCR processin g was unnecessary. We conclude that real-time quantitative PCR monitoring o f peripheral blood can be used to reliably monitor disease response in CML.