Background: Older adults are under-represented in cancer clinical trials. However, it remains unclear which types of trials under-enroll aging patients. We aimed to identify associations between trial characteristics and disparate enrollment of older adults onto trials sponsored by the Alliance for Clinical Trials in Oncology (Alliance).
Methods: Actual age ≥ 65 percentage and trial data were extracted from the Alliance closed study list. Each trial, based on its cancer type and years of enrollment, was assigned an expected age ≥ 65 percentage extracted from the Surveillance, Epidemiology, and End Results (SEER) US population-based database. Enrollment disparity difference (EDD), the difference between the expected age ≥ 65 percentage and the actual age ≥ 65 percentage, was calculated for each trial. Linear regression determined trial variables associated with larger EDDs and variables with an overall association p-value <0.20 were included in a multivariable fixed-effects linear model.
Results: The median age of 66,708 patients across 237 trials was 60 years (range 18-102). The average actual age ≥ 65 percentage enrolled per trial was lower than each trial's expected age ≥ 65 percentage average (39% vs. 58%; EDD 19, 95% CI 17.1-21.3%, p < 0.0001). In multivariable analyses, non-genitourinary (GU) cancer types (p < 0.001), trimodality+ trials (estimate 8.78, 95%CI 2.21-15.34, p = 0.009), and phase 2 trials (estimate 4.43 95% CI -0.06-8.91; p = 0.05) were all associated with larger EDDs.
Conclusions: Disparate enrollment of older adults is not equal across cancer trials. Future strategies to improve older adult inclusion should focus on trial types associated with the highest disparate enrollment.
Keywords: Cancer; Clinical trials; Enrollment; Older adults.
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