Objective: To quantify bone marrow bcr/abl mRNA levels in imatinib mesylate treated Ph chromosome positive chronic myeloid leukemia (CML) patients.
Methods: Serial monitoring of bcr/abl mRNA levels by real-time quantitative RT-PCR technique (RQ-PCR) was performed in 34 cases (120 samples) of CML treated with imatinib mesylate. All the patients were IFNalpha based treatment failure before enrolled in this study and the percentage of Ph(+) bone marrow cells were over 95%.
Results: The sensitivity of RQ-PCR was 10 pg RNA, with both coefficients of interassay and intraassay variation below 5% for standard samples. The median bcr/abl mRNA level of 10 patients' samples pre imatinib treatment was 5.79% with marked variation (0.24%-60.90%). In 72 samples post imatinib treatment, which the rates of Ph(+) cells [Ph(+)%] were between 0 and 94%, the mRNA level well correlated with Ph(+)% (r = 0.82, P < 0.001). The mRNA levels of 7 patients who achieved complete cytogenetic response (CCyR) within 12 months decreased markedly, the levels of 6 analysable patients decreased by 65.9% - 98.8% after 3 months'treatment accordingly. The level further decreased to 0 after achieving CCyR. For 4 patients who achieved major cytogenetic response (Ph(+) cells < 35%) later than 12 months, the mRNA levels decreased slowly. The levels of 3 analysable patients on 3 month therapy decreased by 2.5%, 18.5% and 61.6% compared with that before treatment. Out of 5 patients in chronic phase without cytogenetic response, 1 decreased, 2 increased gradually and 2 had no change. In 4 disease progression patients, the levels increased stepwise.
Conclusions: Serial quantifications of bcr/abl mRNA levels are necessary for imatinib treated patients, and are more informative than a single detection. A sharp decline of bcr/abl mRNA levels after the treatment implies a promise of CCyR.