Maintaining Imatinib ≥600 Mg Daily in the First 12 Months of Chronic Phase CML Treatment Is Associated with Superior Event-Free Survival at 5 Years.

Abstract 1125

Poster Board I-147

The Australasian Leukaemia and Lymphoma Group conducted a trial (TIDEL I) in 103 patients with newly diagnosed chronic phase CML, using imatinib 600 mg/day with dose escalation to 800 mg/day for suboptimal response. This was defined as failure to achieve (1) complete haematological response (CHR) at 3 months, (2) major cytogenetic response (MCR) at 6 months, (3) complete cytogenetic response (CCR) or molecular equivalent at 9 months, or (4) less than 0.01% (IS) BCR-ABL by RQ-PCR at 12 months. Here we report the outcomes with all surviving patients having been treated for at least 60 months. We aimed to determine whether the patient outcome at 60 months was predicted by the molecular response within the first 18 months of imatinib therapy. The outcomes for patients maintaining a dose of imatinib of ≥600 mg/day in the first 12 months was compared to those who were on a reduced dose for at least part of this time. Event-free survival (EFS) was defined as death from any cause, accelerated phase/blast crisis (AP/BC), and loss of CHR, MCR or CCR. The 103 patients included 66 males and 37 females with a median (±SD) age of 49 (±14) years. All patients had an ECOG performance status of 0-2 at enrolment.

The 5-year EFS was 71%, transformation (AP/BC) free survival (TFS) was 95%, and overall survival was 87%. Of the 14 patients who died, 3 died in blast crisis, 2 from transplant-related complications, 8 from CML-unrelated causes, and the cause of death of 1 patient was unavailable. The annual rates of progression to AP/BC over 5 years were 3%, 1%, 0%, 1%, and 0%, while annual event rates were 13%, 8%, 8%, 1%, and 4%. CCR was achieved by 89% of patients by 60 months, while 72% achieved a major molecular response (MMR) by this time.

In the first 12 months of treatment, 55% of patients maintained an imatinib dose of ≥600 mg/day (mean ±SD dose = 604 ±10 mg/day), while 45% were on <600 mg/day for at least part of this time (mean ±SD dose = 511 ±100 mg/day). EFS at 60 months was significantly higher in patients taking ≥600 mg/day compared with those who had been dose-reduced to <600 mg/day (89% vs 56%, P<0.001). Annual event rates for the ≥600 mg/day group were 6%, 2%, 2%, 0%, and 2%, while annual event rates for those on <600 mg/day were 14%, 16%, 16%, 8%, and 4%. By 60 months, 96% of patients who had been on ≥600 mg/day within the first 12 months had achieved CCR, while only 80% of those who had been on <600 mg/day had achieved this milestone (P<0.001). Log rank analysis of the achievement of MMR was also significant (P=0.03). Overall survival and TFS after 12 months were both similar between the dosing groups. There was no difference between the dosing groups' median age (50 vs 48 years, P=0.36) or Sokal score (1.04 vs 0.94, P=0.33) that may otherwise account for these results.

The outcome was also determined for all patients dependent on the BCR-ABL levels at various assessment timepoints. Patients with a BCR-ABL level of <10% (IS) at 6 months (n=92) had an EFS of 78% at 60 months, while all of those with a level >10% (IS) (n=8) had an event (P<0.001). Patients with a level of ≤1% (IS) at 12 months (equivalent to CCR) (n=81) had an EFS of 75% compared with 25% (n=13) for those with levels >1% (IS) (P<0.001). At 18 months, a level ≤0.1% (IS) (n=58) conferred an EFS of 88%, while those who had failed to attain this depth of response (n=30) had an EFS of 60%. There was a significant difference in EFS between those who had achieved an MMR at 18 months and those who had achieved a CCR, but no MMR (88% vs 67%, P=0.03).

In conclusion, our data suggest that patients maintaining a dose of ≥600mg in the first 12 months of imatinib therapy are more likely to achieve CCR and MMR, and superior EFS compared to those with a lower dose. This study also confirms that achieving an MMR by 18 months is associated with improved EFS. This emphasises the value of achieving a molecular response early in the treatment course, as well as adding weight to the evidence supporting the role of molecular monitoring in CML.