Long Term Adherence to Imatinib Therapy Is the Critical Factor for Achieving Molecular Responses in Chronic Myeloid Leukemia Patients.

Abstract 3290

Poster Board III-1

There is a great variability in the degree of molecular responses achieved by chronic myeloid leukemia (CML) patients treated with imatinib. These different levels of molecular response could reflect different degrees of adherence to therapy. We measured the adherence to imatinib therapy in 87 consecutive CML chronic phase patients who had received imatinib 400 mg day as first line therapy for a median of 59.7 months before enrolment (range 25–104) and therefore all them were in complete cytogenetic response. Adherence levels were monitored during a 3-month period using microelectronic monitoring devices (MEMS) and were related to levels of molecular response. MEMS consist of an electronic device fitted in the cap of a normal looking medication bottle that automatically records each time the bottle is opened. MEMS are considered as the ‘gold standard' for measuring adherence. We also measured the imatinib plasma level, the presence of TKD mutations and the following prognostic factors measured at diagnosis: hOCT1 transcripts level, polymorphism 1236C>T in ABCB1, Sokal risk group, hemoglobin, leukocytes , BCR-ABL1 transcript type and BCR1-ABL1 ratio and demographic data. The study protocol was approved by the Research Ethics Committee and patients gave written informed consent to participate.

The median adherence rate was 97.6% (range 22.6–103.8%). In 23 (26.4%) patients adherence was ≤90% (median 76%) and in 12 (13.8%) ≤80% (median 63%). We found a strong association between adherence rate (≤90% or >90%) and the 6-year probability of major molecular response (MMR) (28.4% vs 94.5%, p<0.0001) and complete molecular response (CMR) (0% vs 43.8%, p=0.002) (Fig 1). Multivariate analysis identified adherence (RR=11.7, p=0.001) and expression of the molecular transporter hOCT1, (RR=1.79, p=0.038) as the only independent predictors for MMR. Adherence was the sole independent predictor for CMR. No molecular responses were observed when the adherence was ≤20% (p=0.0001). In patients whose imatinib dose had been increased (n=32) the adherence was poor (median 86.4%). Adherence was the only independent predictor for failure to achieve a 3-log transcript reduction (RR=17.66, p=0.006) in this subgroup of patients. Patients with CML vary greatly in their response, as demonstrated originally by Sokal et al. in 1984, and the same variation is seen in patients treated with imatinib in the modern era. The basis for this variation is unknown but it has been attributed to the intrinsic biological heterogeneity of the leukemia. In contrast we show here that adherence to therapy is the major factor determining the degree of response that a CML patient treated with imatinib will achieve.

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