Final Results of the OPTIM-Imatinib Study in Patients with CP-CML

Imatinib mesylate (IM) at 400 mg/day is the standard of care as first-line therapy in patients with newly diagnosed, chronic-phase chronic myeloid leukemia (CP-CML). Based on evidence that patients with high imatinib trough levels achieved higher rates of major molecular response (MMR), the randomized OPTIM-imatinib trial was conducted to evaluate the value of imatinib dose optimization according to imatinib C_min levels in newly diagnosed patients with CP-CML.^1,2

Based on imatinib C_min levels, as determined by chromatography–tandem mass–mass spectrometry 15 days after enrollment, patients with a C_min level <1000 ng/mL were randomized to 2 arms: a dose-increase strategy with dose adjustment every 4 weeks aiming to reach the threshold of 1000 ng/mL (arm A1) versus standard IM management (arm A2); patients with imatinib C_min levels ≥1000 ng/mL were observed on imatinib 400 mg/day (arm A3).

Of the 133 evaluable patients, 64% showed initial C_min <1000 ng/mL and were randomized between arms A1 (n = 43) and A2 (n = 43), while the 47 remaining patients with C_min ≥1000 ng/mL were observed in arm A3. Overall, 36% of patients with C_min ≥1000 ng/mL are well-dosed with imatinib 400 mg/day. Following dose adjustment in arm A1, there was a significant improvement in median imatinib C_min compared with standard management in arm A2 (P <.0001). In arm A1, the imatinib daily dose increased to reach a mean value of 600 mg/day, indicating that the majority of patients were not exposed enough to imatinib at standard dose.

The rates of adverse events were similar between arms A1 (58%) and A2 (51%). Treatment discontinuations were also comparable among the 3 arms, reaching 34.1% by 24 months. At 12 months, a higher proportion of patients in arm A1 achieved the primary end point of MMR compared with arm A2 (76% vs 44%; P = .002); however, the MMR rate was numerically lower in arm A2 compared with the standard arm A3 (44% vs 56%).

Based on these results, the authors concluded that individualized dose-adjustment strategies based on pharmacology may be required to optimize the outcome for each patient.

References

1. Larson RA, Druker BJ, Guilhot F, et al. Imatinib pharmacokinetics and its correlation with response and safety in chronic-phase chronic myeloid leukemia: a subanalysis of the IRIS study. Blood. 2008;111:4022-4028.
2. Rousselot P, Johnson-Ansah H, Huguet F, et al. Personalized daily doses of imatinib by therapeutic drug monitoring increase the rates of molecular responses in patients with chronic myeloid leukemia. Final results of the randomized OPTIM imatinib study. Blood. 2015;126:133.