Imatinib plasma levels: correlation with clinical benefit in GIST patients

The issue of suitability of therapeutic drug monitoring (TDM) for imatinib continues to fuel controversies. Unlike two previous studies in gastrointestinal stromal tumours (GIST) patients ( Judson et al, 2005 ; Delbaldo et al, 2006 ), a recent clinical pharmacokinetic (PK) substudy carried out on the basis of the B2222 trial, evaluating imatinib in patients with unresectable or metastatic CD117-positive GIST, found a correlation between imatinib total exposure and clinical response. Trough levels over 1100 ng ml −1 predicted a better overall benefit rate (composite clinical outcome; Demetri et al, 2009 ). These results are thus in line with observations made in CML patients, showing trough levels over 1000 ng ml −1 to predict a better molecular response rate ( Picard et al, 2007 ; Larson et al, 2008 ).