Journal
JOURNAL OF CLINICAL ONCOLOGY
Volume 30, Issue 17, Pages 2094-2101Publisher
AMER SOC CLINICAL ONCOLOGY
DOI: 10.1200/JCO.2011.38.9924
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Funding
- National Institutes of Health [R01 CA096670, M01-RR00043, U10 CA098543, U10 CA095861, R37 CA36401, CA 21765]
- American Lebanese Syrian Associated Charities
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Purpose Systemic exposure to mercaptopurine (MP) is critical for durable remissions in children with acute lymphoblastic leukemia (ALL). Nonadherence to oral MP could increase relapse risk and also contribute to inferior outcome in Hispanics. This study identified determinants of adherence and described impact of adherence on relapse, both overall and by ethnicity. Patients and Methods A total of 327 children with ALL (169 Hispanic; 158 non-Hispanic white) participated. Medication event-monitoring system caps recorded date and time of MP bottle openings. Adherence rate, calculated monthly, was defined as ratio of days of MP bottle opening to days when MP was prescribed. Results After 53,394 person-days of monitoring, adherence declined from 94.7% (month 1) to 90.2% (month 6; P = .001). Mean adherence over 6 months was significantly lower among Hispanics (88.4% v 94.8%; P < .001), patients age >= 12 years (85.8% v 93.1%; P < .001), and patients from single-mother households (80.6% v 93.1%; P = .001). A progressive increase in relapse was observed with decreasing adherence (reference: adherence >= 95%; 94.9% to 90%: hazard ratio [HR], 4.1; 95% CI, 1.2 to 13.5; P = .02; 89.9% to 85%: HR, 4.0; 95% CI, 1.0 to 15.5; P = .04; < 85%: HR. 5.7; 95% CI, 1.9 to 16.8; P = .002). Cumulative incidence of relapse (+/- standard deviation) was higher among Hispanics (16.5% +/- 4.0% v 6.3% +/- 2.2%; P = .02). Association between Hispanic ethnicity and relapse (HR, 2.6; 95% CI, 1.1 to 6.1; P = .02) became nonsignificant (HR, 1.8; 95% CI, 0.6 to 5.2; P = .26) after adjusting for adherence and socioeconomic status. At adherence rates >= 90%, Hispanics continued to demonstrate higher relapse, whereas at rates < 90%, relapse risk was comparable to that of non-Hispanic whites. Conclusion Lower adherence to oral MP increases relapse risk. Ethnic difference in relapse risk differs by level of adherence-an observation currently under investigation.
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