6MP adherence in a multiracial cohort of children with acute lymphoblastic leukemia: a Children's Oncology Group study

Durable remissions in children with acute lymphoblastic leukemia (ALL) require a 2‐year maintenancephase that includesdailyoral 6‐mercaptopurine (6MP).Adherenceto oral6MP among Asian‐American and African‐American children with ALL is unknown. We enrolled 298 children with ALL (71 Asian Americans, 68 African Americans, and 159 non‐Hispanic whites) receiving oral 6MP for the maintenance phase. Adherence was measured electronically for 39 803 person‐days. Adherence declined from 95.0% (month 1) to 91.8% (month 5, P < .0001). Adherence rates were significantly (P < .0001) lower in Asian Americans (90.0% + 4.9%) and African Americans (87.1% + 4.4%), as compared with non‐Hispanic whites (95.2% + 1.3%). Race‐specific sociodemographic characteristics helped explain poor adherence (African Americans: low maternal education [less than a college degree: 78.9%, vs at least college degree: 94.6%; P < .0001]; Asian Americans: low‐income households [<$50 000: 84.5%, vs ++$50 000: 96.7%; P = .04]; households without mothers as full‐time caregivers [85.6%] vs households with mothers as full‐time caregivers [97.2%; P = .05]). Adherence rate below 90% was associated with increased relapse risk (hazard ratio, 3.9; P = .01). Using an adherence rate <90% to define nonadherence, 20.5% of the participants were nonadherers. We identify race‐specific determinants of adherence, and define a clinically relevant level of adherence needed to minimize relapse risk in a multiracial cohort of children with ALL. This trial was registered at www.clinicaltrials.gov as #NCT00268528.