The differences and correlations of BCR-ABL transcripts between peripheral blood and bone marrow assays are associated with the molecular responses in the bone marrow for chronic myelogenous leukemia.

Previous studies concerning BCR-ABL mRNA levels by quantitative real-time RT-PCR (Q-PCR) for chronic myelogenous leukemia (CML) have shown a significant concordance between peripheral blood (PB) and bone marrow (BM) assays. The objective of this study was to determine whether molecular monitoring using PB was comparable to using BM for CML. A comparative study was performed that analyzed the Q-PCR results of 712 simultaneous PB and BM samples from 330 patients before and during imatinib therapy. For the 78 paired pretreatment samples, the level of BCR-ABL mRNA in PB was lower than that in BM (P = 0.007). Although the overall amounts of BCR-ABL mRNA in the PB and BM were comparable (P= 0.072) and there was a strong correlation (r = 0.839, P < 0.001) with the 634 paired on-treatment samples, the depth of the molecular response in PB was lower than that in BM (P < 0.001). The level of BCR-ABL mRNA in PB was lower than that in BM where the BM BCR-ABL mRNA < 1 log reduction (P < 0.001) or ≥ 1-< 2 log-reductions (P = 0.008) from the baseline, and higher than that where the BM BCR-ABL mRNA ≥ 2 log-reductions (P < 0.001). A strong correlation (r = 0.811, P < 0.001) was only found where the BM BCR-ABL mRNA < 1 log reduction. We conclude that the differences and correlations of BCR-ABL mRNA between PB and BM assays depend on the depth of the molecular response in BM for CML during imatinib therapy.