LAUSR

The association between individual-level poverty and relapse in children receiving maintenance treatment for acute lymphoblastic leukemia (ALL) remains unclear. In a secondary analysis of COG-AALL03N1, we used data from US Census Bureau to categorize patients living below year-specific federal poverty thresholds, calculated using self-reported annual household income and size of household. Participants living 120% below federal poverty thresholds were categorized as living in extreme poverty. Hazard of relapse was estimated using multivariable proportional subdistributional hazards regression for patients living in extreme poverty while receiving ALL maintenance therapy after adjusting for relevant predictors. Among 592 patients in this analysis, 12.3% of the patients were living in extreme poverty. After a median follow-up of 7.9y, the cumulative incidence of relapse at 3y from study enrollment among those living in extreme poverty was significantly higher (14.3%, 95% confidence interval [CI]= 7.3-23.6) compared to those not living in extreme poverty (7.6%, 95%CI=5.5-10.1, P=0.04). Multivariable analysis demonstrated that children living in extreme poverty had a 1.95-fold greater hazard of relapse (95%CI=1.03-3.72, P=0.04) compared to those not living in extreme poverty; this association was mitigated after inclusion of race/ethnicity in the model (hazard ratio=1.68, 95%CI=0.86-3.28, P=0.1), likely due to collinearity between race/ethnicity and poverty. A greater proportion of children living in extreme poverty were non-adherent to mercaptopurine (57.1% vs 40.9%, P=0.04); however, poor adherence did not completely explain the association between poverty and relapse risk. Future studies need to understand the mechanisms underlying the association between extreme poverty and relapse risk. Clinical Trial number: NCT00268528.