Outcomes by Cytogenetic and Molecular Response at 12 and 18 Months of Imatinib in Patients with Newly Diagnosed Chronic Myeloid Leukemia (CML) in Chronic Phase (CP) in the IRIS Trial.

Long term data is now available from the International Randomized Study of Interferon vs. STI571 (IRIS). We performed landmark analyses for pts on imatinib (IM) at 12 and 18 months (mos) (n=509 and n=480 respectively) and stratified for CCyR (Ph+ 0%), PCyR (Ph+ >0–35%) or No MCyR (Ph+ >35%) at both timepoints. Progression-free survival (PFS) included all progressions to accelerated phase or blast crisis during treatment with IM, whereas event-free survival (EFS) also included any loss of MCyR/CHR, increase in WBC and CML-unrelated deaths on treatment as events. Overall survival (OS) considered all deaths including those after discontinuation of IM and irrespective of whether pts went on to transplant.

Although the level of cytogenetic response was predictive for long-term outcomes, PFS and OS were not statistically significantly different between 12-mos CCyR and PCyR. Note that 64% of PCyR pts and 36% of pts without MCyR at 12 mos subsequently achieved CCyR. Using the 18-mos landmark, 50% of PCyR pts and 27% of pts without MCyR achieved CCyR at a later time. Long-term outcomes were evaluated based on available BCR-ABL transcript levels in pts with CCyR. A 3-log reduction from standardized baseline value in untreated pts was defined as a major molecular response (MMR). No pts who achieved both CCyR and MMR at 12 or 18 mos progressed to AP/BC by 60 mos. Approximately 5% of pts with CCyR but no MMR at 12 mos (p=0.007) and only 2% of CCyR pts without MMR at 18 mos (p=0.11) subsequently progressed. Of approximately 25% of CCyR pts with available PCR analysis who did not achieve MMR at 18 mos, about half did achieve MMR at a later time and their estimated EFS rate at 60 mths was 91%.

At 60 mos, 69% of patients randomized to IM remained on treatment. Achievement of CCyR and MMR by 12 and 18 mos after start of IM in newly diagnosed CML-CP are predictive for favorable long-term outcomes. About 50% of pts in PCyR or CCyR at these time points eventually achieve CCyR and MMR, respectively, on continued IM treatment. The ability to identify patients who may be late responders should be further studied.