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Background: Outcomes in pediatric acute lymphoblastic leukemia (ALL) have shown remarkable improvements in large part due to sequential clinical trials. Concerns however persist around whether access to clinical trials is equitable. It is also unclear whether patient outcomes are improved simply by enrolling on a clinical trial. Our objective was to therefore determine which patient and disease-related factors are associated with enrollment, and whether enrollment was associated with clinical outcomes among children and adolescents with ALL in a single-payer health system in Ontario, Canada. Methods: We included all Ontario patients diagnosed with ALL between 0-18 years of age from 2002-2012 treated at a pediatric center, identified through a provincial pediatric cancer registry. Clinical trial availability was determined by whether each patient’s primary institution had an open frontline trial for which the patient was eligible at the time of their diagnosis, considering individual disease characteristics such as lineage, central nervous system (CNS) status and risk group. Demographic, disease, trial enrolment, and outcome data were obtained through chart abstraction. Logistic regression models determined factors associated with trial enrolment, while Cox proportional hazard models determined factors associated with event-free and overall survival (EFS, OS). Results: Of 858 patients, 693 (81%) were eligible for an open clinical trial at their time of diagnosis. 476 (69%) enrolled on a trial. In adjusted analyses, age > 15 years (odds ratio 0.4 vs. age 5-9, 95
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confidence interval (95CI) 0.2-0.8; p = 0.01) and CNS3 disease (OR 0.38 vs. CNS1, 95CI 0.17-0.83; p = 0.01) were significantly associated with decreased likelihood of enrolment, while sex and neighborhood income quintile were not associated with enrolment. Adjusted for disease and demographic factors, clinical trial enrolment was not significantly associated with either EFS (hazard ratio (HR) 1.1, 95CI 0.7-1.7; p = 0.83) or OS (HR 1.3, 95CI 0.7-2.5; p = 0.44). Conclusions: The majority of patients with ALL eligible for available clinical trials at their time of diagnosis were enrolled. While no disparities in enrolment by income status were noted, adolescents were substantially less likely to participate in trials even within pediatric centers. Studies of mechanisms underlying this disparity are warranted in order to design and implement effective interventions targeting increased enrolment rates in this patient population. Our results however also suggest that clinical trial enrolment on its own is not associated with improved outcomes in the context of a single payer health system.