Control group design, contamination and drop-out in exercise oncology trials: a systematic review.

Charlotte N Steins Bisschop,Christine Friedenreich,Miranda J Velthuis,Kerry S Courneya,Anne M May,Lee W Jones,Elsken Van Der Wall,Evelyn M Monninkhof,Petra H M Peeters,Roberta W Scherer

doi:10.1371/journal.pone.0120996

Abstract

PurposeImportant considerations for exercise trials in cancer patients are contamination and differential drop-out among the control group members that might jeopardize the internal validity. This systematic review provides an overview of different control groups design characteristics of exercise-oncology trials and explores the association with contamination and drop-out rates.MethodsRandomized controlled exercise-oncology trials from two Cochrane reviews were included. Additionally, a computer-aided search using Medline (Pubmed), Embase and CINAHL was conducted after completion date of the Cochrane reviews. Eligible studies were classified according to three control group design characteristics: the exercise instruction given to controls before start of the study (exercise allowed or not); and the intervention the control group was offered during (any (e.g., education sessions or telephone contacts) or none) or after (any (e.g., cross-over or exercise instruction) or none) the intervention period. Contamination (yes or no) and excess drop-out rates (i.e., drop-out rate of the control group minus the drop-out rate exercise group) were described according to the three design characteristics of the control group and according to the combinations of these three characteristics; so we additionally made subgroups based on combinations of type and timing of instructions received.Results40 exercise-oncology trials were included based on pre-specified eligibility criteria. The lowest contamination (7.1% of studies) and low drop-out rates (excess drop-out rate -4.7±9.2) were found in control groups offered an intervention after the intervention period. When control groups were offered an intervention both during and after the intervention period, contamination (0%) and excess drop-out rates (-10.0±12.8%) were even lower.ConclusionsControl groups receiving an intervention during and after the study intervention period have lower contamination and drop-out rates. The present findings can be considered when designing future exercise-oncology trials.

Highlights

There is growing evidence for beneficial effects of physical exercise in patients with cancer [1,2,3]
Pooled results of exercise oncology trials focusing on supervised and home-based exercise programs in several meta-analyses showed that exercise during and after cancer treatment is beneficial in terms of improved quality of life, physical fitness, reduced cancer-related fatigue and anxiety and depression [1,2,3]
Cancer patients participating in an exercise trial are highly motivated to exercise and, participants randomized to the control group may increase their physical activity levels

Summary

Introduction

There is growing evidence for beneficial effects of physical exercise in patients with cancer [1,2,3]. In many exercise-oncology trials, patients are randomized to either an exercise intervention or a usual care (i.e., no exercise) control group. Cancer patients participating in an exercise trial are highly motivated to exercise and, participants randomized to the control group may increase their physical activity levels. They often change their behavior despite the request to maintain their usual activity pattern [6]. This non-compliance by controls may lead to a decrease of power to detect a significant intervention effect. Patients who first agreed to participate may drop out after being randomized to the control group

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Methods

Conclusion