Molecular response to imatinib mesylate of Brazilian patients with chronic myeloid leukemia

Background: Imatinib mesylate has revolutionized the treatment of chronic myeloid leukemia leading to significant reductions of BCR-ABL1 transcript levels in peripheral blood.

Objective: To evaluate the response to imatinib mesylate treatment (400mg/day) in Brazilian patients in the chronic phase of chronic myeloid leukemia monitored by quantitative real time polymerase chain reaction.

Methods: Between October 2002 and October 2010, 3169 peripheral blood samples were collected from 1403 patients from 3 to 5 months, 6 to 11 months, 12 to 17 months, 18 to 23 months and ≥24 months after beginning imatinib treatment. Eighty-two patients had samples available and analyzed for all time intervals. BCR-ABL1 quantification was performed by quantitative real time polymerase chain reaction using the ABL1 gene as the control. Results of the BCR-ABL1 ratio as a percentage were reported by the international scale (IS) using the laboratory conversion factor (0.51).

Results: In the first interval, 80.8% of patients achieved the optimal response (BCR-ABL1^IS≤10%). In the second period, 69.1% achieved optimal response (BCR-ABL1^IS≤1%) and, between 12 and 17 months, 47.3% achieved major molecular response (BCR-ABL1^IS≤0.1%).

Conclusions: The results of this retrospective study show that the response to imatinib treatment (400mg/day) of Brazilian patients in the chronic phase of chronic myeloid leukemia is within the expected profile when compared to patients reported in international prospective randomized studies.