Rates of and Factors Associated with Patient Withdrawal of Consent in Cancer Clinical Trials

Importance: Patient withdrawal of consent from a cancer clinical trial is defined as a patient's volitional cessation of participation in all matters related to a trial. It can undermine the trial's purpose, make the original sample size and power calculations irrelevant, introduce bias between trial arms, and prolong the time to trial completion. Objective: To report rates of and baseline factors associated with withdrawal of consent among patients in cancer clinical trials. Design, Setting, and Participants: This multisite observational cohort study was conducted through the Alliance for Clinical Trials in Oncology. Patient withdrawal was defined as a patient's voluntary termination of consent to participate anytime during trial conduct. Baseline patient- and trial-based factors were investigated for their associations with patient withdrawal within the first 2 years using logistic regression models. All patients who participated in cancer therapeutic clinical trials conducted within the Alliance for Clinical Trials in Oncology from 2013 through 2019 were included. The data lock date was January 23, 2022. Main Outcomes and Measures: The percentage of patients who withdrew consent in 2 years and factors associated with withdrawal of consent. Results: A total of 11993 patients (median age, 62 years; 67% female) from 58 trials were included. Within 2 years, 1060 patients (9%) withdrew from their respective trials. Two-year rates of withdrawal were 5.7%, 7.6%, 8.5%, 7.8%, 8.4%, 9.5%, and 9.8% for each of the respective years from 2013 through 2019. In multivariable analyses, Hispanic ethnicity (odds ratio [OR], 1.67; 95% CI, 1.30-2.15; P <.001), randomized design with placebo (OR, 1.64; 95% CI, 1.38-1.94; P <.001), and patient age 75 years and older (OR, 1.39; 95% CI, 1.12-1.72; P =.003) were associated with higher likelihood of withdrawal by 2 years. Use of radiation was associated with patient retention (OR, 0.68; 95% CI, 0.54-0.86; P =.001). Conclusions and Relevance: In this cohort study, rates of withdrawal of consent were less than 10% and appeared consistent over time. Factors that are associated with withdrawal of consent should be considered when designing trials and should be further studied to learn how they can be favorably modified..