• Roxanne Gal, Evelyn M Monninkhof, Carla H van Gils, Groenwold Rolf H H RHH Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands., Desirée H J G van den Bongard, Peeters Petra H M PHM Department of Clinical Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utre, Helena M Verkooijen, and Anne M May.
• Department of Clinical Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands.
• J Clin Epidemiol. 2019 Sep 1; 113: 137-146.

ObjectivesThe Trials within Cohorts (TwiCs) design is an alternative for pragmatic randomized controlled trials (RCTs) and might overcome disadvantages such as difficult recruitment, dropout after randomization to control, and contamination. We investigated the applicability of the TwiCs design in an exercise oncology study regarding the recruitment process, representativeness of the study sample, contamination, participation, and dropout.MethodsThe Utrecht cohort for Multiple BREast cancer intervention studies and Long-term evaLuAtion (UMBRELLA) Fit TwiCs evaluates an exercise intervention in inactive breast cancer patients. Eligible patients participating in the prospective UMBRELLA were identified and randomized. Patients randomized to the intervention (n = 130) were offered the intervention, whereas controls (n = 130) were not informed.ResultsFifty-two percent (n = 68) accepted the intervention. Because this rate was lower than expected, a larger sample size was required than initially estimated (n = 166). However, recruitment of 260 patients was still completed by one researcher within 30 months. Unselective eligibility screening and randomization before invitation improved representativeness. Disadvantage of the design might be inclusion of ineligible patients when cohort information is limited. Furthermore, the design faced higher noncompliance in the intervention group, but prevention of contamination.ConclusionThe TwiCs design improved logistics in recruitment and prevented contamination, but noncompliance due to refusal of the intervention was higher compared with conventional pragmatic exercise oncology RCTs, which may dilute the estimated intervention effect.Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.

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