Purpose: This study assessed whether a cycle of "routine” therapeutic drug monitoring (TDM) for imatinib dosage individualization, targeting an imatinib trough plasma concentration (C min) of 1,000ng/ml (tolerance: 750-1,500ng/ml), could improve clinical outcomes in chronic myelogenous leukemia (CML) patients, compared with TDM use only in case of problems ("rescue” TDM). Methods: Imatinib concentration monitoring evaluation was a multicenter randomized controlled trial including adult patients in chronic or accelerated phase CML receiving imatinib since less than 5years. Patients were allocated 1:1 to "routine TDM” or "rescue TDM.” The primary endpoint was a combined outcome (failure- and toxicity-free survival with continuation on imatinib) over 1-year follow-up, analyzed in intention-to-treat (ISRCTN31181395). Results: Among 56 patients (55 evaluable), 14/27 (52%) receiving "routine TDM” remained event-free versus 16/28 (57%) "rescue TDM” controls (P=0.69). In the "routine TDM” arm, dosage recommendations were correctly adopted in 14 patients (median C min: 895ng/ml), who had fewer unfavorable events (28%) than the 13 not receiving the advised dosage (77%; P=0.03; median C min: 648ng/ml). Conclusions: This first target concentration intervention trial could not formally demonstrate a benefit of "routine TDM” because of small patient number and surprisingly limited prescriber's adherence to dosage recommendations. Favorable outcomes were, however, found in patients actually elected for target dosing. This study thus shows first prospective indication for TDM being a useful tool to guide drug dosage and shift decisions. The study design and analysis provide an interesting paradigm for future randomized TDM trials on targeted anticancer agents
