Significance of Suboptimal Response to Imatinib, as Defined by the European LeukemiaNet, in Long-Term Outcome for Patients (Pts) with Chronic Phase (CP) Chronic Myeloid Leukemia (CML).

Abstract

The European LeukemiaNet recently published recommendations for evaluating response to imatinib among pts with CML. Criteria for failure and suboptimal responses were proposed. The significance of failure is accepted and constitutes grounds for change in treatment. The prognostic implications of having a suboptimal response are less clear making treatment decisions less clear in this setting. We analyzed the outcome of 281 pts treated with imatinib as frontline therapy for CML in CP: 73 at initial dose of 400mg daily and 208 at 800mg daily. Their median age was 48 yrs (range, 15 to 84 yrs) and their median follow-up 48 months (mo) (2–79 mo). After 3 mo of therapy none of the 273 evaluable pts met definition of suboptimal response according to the European LeukemiaNet, while 3 of 273 (1%) met definition for failure. At 6 mo 10/259 (4%) evaluable had suboptimal response and 9 (3%) failure. At 12 mo 19/246 (8%) had suboptimal and 14 (6%) failure, and at 18 mo 91/224 (41%) had suboptimal and 21 (9%) had failure. The probability of having a suboptimal response at 6 and 12 mo was significantly higher for pts treated with a starting dose of 400mg than those treated at 800mg: at 6 mo [12% suboptimal at 400mg vs 1% at 800mg (p=0.002)] and at 12 mo [17% and 4%, respectively (p<0.001)]. The outcome at 24 months* by the response at specific times was as follows:TimeResponse% CCyR% MMR% Transf% Event6 moOptimal916026Suboptimal003050Failure002267P.001.001.001.00112 moOptimal946324Suboptimal5625016Failure002157P.001.001.001.00118 moOptimal988501Suboptimal933925Failure1501943P.001.001.001.001CCyR=Complete cytogenetic remission, MMR=Major molecular remission, Transf=Transformation to accelerated or blast phase, Event=loss of complete hematologic response, loss of major cytogenetic response, transformation, or death