Trough plasma imatinib levels are correlated with optimal cytogenetic responses at 6 months after treatment with standard dose of imatinib in newly diagnosed chronic myeloid leukemia.

To investigate the correlation of trough imatinib mesylate (IM) levels with cytogenetic or molecular responses, we measured trough IM levels in patients with chronic myeloid leukemia, chronic phase (CML-CP), at 6 months of treatment with a standard dose of IM. Eighty-seven newly diagnosed patients with CML-CP were prospectively enrolled. Seventy-eight patients (89.7%) showed an optimal response (complete or partial cytogenetic response) at 6 months. Trough IM levels were 1378 ± 725 ng/mL. When categorized into two groups, there was a statistically significant difference in numbers of patients with optimal and suboptimal responses at 6 months (group with  <1000: 80.6% vs. 19.4%;  ≥ 1000: 94.6% vs. 5.4%; p = 0.032), and in numbers of patients with early major molecular response (early-MMR) and without MMR at 6 months (group with  <1000: 3.2% vs. 96.8%;  ≥ 1000: 21.4% vs. 78.6%; p = 0.047). In conclusion, the incidence of optimal cytogenetic response or early-MMR in patients with CML-CP treated with IM for 6 months was significantly higher in those with a trough level of  ≥ 1000 compared with those with a level of <1000. Dose escalation of IM can be one option in patients with CML showing suboptimal response or resistance to the standard dose of IM, especially with low trough plasma IM levels (<1000 ng/mL).