Comparison of self-report and electronic monitoring of 6MP intake in childhood ALL: A Children's Oncology Group study

Wendy Landier, Yanjun Chen, Lindsey Hageman, Heeyoung Kim, Bruce C. Bostrom, Jacqueline N. Casillas, David S. Dickens, William E. Evans, Kelly W. Maloney, Leo Mascarenhas, A. Kim Ritchey, Amanda M. Termuhlen, William L. Carroll, Mary V. Relling, F. Lennie Wong and Smita Bhatia

Key points

  • Self-report over-estimated electronically monitored 6MP adherence at least some of the time in the large majority (84.4%) of patients.

  • Non-adherers were more likely to over-report 6MP intake (47%) compared with adherent patients (8%).


Adequate exposure to oral 6-mercaptopurine (6MP) during maintenance therapy for childhood acute lymphoblastic leukemia (ALL) is critical for sustaining durable remissions; the accuracy of self-reported 6MP intake is unknown. We aimed to directly compare self-report to electronic monitoring (Medication Event Monitoring System [MEMS]), and identify predictors of over-reporting in a cohort of 416 children with ALL in first remission over 4 study months per patient (1,344 patient-months for the cohort) during maintenance therapy. Patients were classified as "perfect reporters" (self-report=MEMS), "over reporters" (self-report>MEMS by ≥5 days/month for ≥50% of study months), and "others" (all patients not meeting criteria for perfect- or over-reporter). Multivariable logistic regression examined sociodemographic and clinical characteristics, 6MP dose-intensity, TPMT genotype, TGN levels, and 6MP non-adherence (MEMs-based adherence rate <95%) associated with the over-reporter phenotype; generalized estimating equations (GEE) compared 6MP intake by self-report and MEMS over the study period. Self-reported 6MP intake exceeded MEMS at least some of the time in 84% of patients. Fifty (12%) patients were classified as perfect reporters, 98 (23.6%) as over-reporters, 2 (0.5%) as under-reporters, and 266 (63.9%) as others. Multivariable logistic regression technique identified the following variables associated with the over-reporter phenotype: i) non-white race: Hispanic, odds ratio (OR)=2.4, 95%CI, 1.1-5.1, p=0.02; Asian, OR=3.1, 95%CI, 1.2-8.3, p=0.02; African-American, OR=5.4, 95%CI, 2.3-12.8, p=0.0001; ii) paternal education <college (OR=1.4, 95%CI, 1.0-2.0, p=0.05); and iii) 6MP non-adherence (OR=9.4, 95%CI, 5.1-17.5, p<0.0001). Self-report of 6MP intake in childhood ALL over-estimates true intake, particularly in non-adherent patients, and should be used with caution.

  • Submitted July 11, 2016.
  • Accepted December 29, 2016.