Nonadherence to Oral 6-Mercaptopurine (6MP) in a Multi-Ethnic Cohort of Children with Acute Lymphoblastic Leukemia (ALL) and Its Impact On Relapse – a Children's Oncology Group (COG) Study (AALL03N1)

Abstract 882 Background: Nearly 20% of children with ALL relapse within 5y from diagnosis. Second-line therapies are toxic and salvage is poor. Systemic exposure to 6MP is critical for durable remissions; low systemic exposure due to nonadherence to oral 6MP could potentially increase relapse risk. We have previously reported on adherence to oral 6MP in non-Hispanic whites and Hispanics, (J Clin Oncol 2012;30:2094-101); this report extends follow-up for assessment of disease status by 68,250 person-days for non-Hispanic whites and Hispanics; it also includes adherence data for a previously unreported cohort of African American and Asian children. The goal of this report was to: i) describe adherence to oral 6MP in a multi-ethnic cohort of children with ALL; ii) identify determinants of adherence; iii) describe impact of adherence on relapse; and iv) define a clinically-relevant level of adherence needed to minimize relapse risk. Methods: Microprocessor chips in Medication Event Monitoring System (MEMS) caps recorded date/time of 6MP bottle openings for 6 mos/ patient. Adherence rate was defined as days of 6MP bottle opening, divided by days of prescribed 6MP (removing days when 6MP was withheld for toxicity/illness from denominator). Monthly red cell thioguanine nucleotide (TGN) levels were used to demonstrate that MEMS bottle openings were accompanied by 6MP ingestion. Analyses used Generalized Estimating Equations. Results: 462 patients (168 Hispanics; 157 non-Hispanic whites; 69 Asians; 68 African Americans) yielded 76,055 person-days of adherence data. Median age at participation was 6y (2-20); 67% were males; 40% had high-risk disease per NCI criteria; 61% reported income Conclusions: Non-adherence to 6MP is prevalent in children with ALL; 45% consume Disclosures: Relling: St. Jude Children's Research Hospital: Dr. Mary Relling receives a portion of the income St. Jude receives from licensing patent rights related to TPMT polymorphisms and GGH polymorphisms. Dr. Mary Relling receives a portion of the income St. Jude receives from licensing patent rights related to TPMT polymorphisms and GGH polymorphisms. Patents & Royalties; Sigma-Tau Pharmaceuticals: Research Funding.