Abstract: We included 23 studies in this review, involving a total of 1372 participants (an addition of 10 studies, 724 participants from the original review); 227 full texts were screened in the update and 377 full texts were screened in the original review leaving 35 publications from a total of 23 unique studies included in the review. We planned to include all cancers, but only studies involving breast, prostate, colorectal and lung cancer met the inclusion criteria. Thirteen studies incorporated a target level of exercise that could meet current recommendations for moderate-intensity aerobic exercise (i.e.150 minutes per week); or resistance exercise (i.e. strength training exercises at least two days per week). Adherence to exercise interventions, which is crucial for understanding treatment dose, is still reported inconsistently. Eight studies reported intervention adherence of 75% or greater to an exercise prescription that met current guidelines. These studies all included a component of supervision: in our analysis of BCTs we designated these studies as 'Tier 1 trials'. Six studies reported intervention adherence of 75% or greater to an aerobic exercise goal that was less than the current guideline recommendations: in our analysis of BCTs we designated these studies as 'Tier 2 trials.' A hierarchy of BCTs was developed for Tier 1 and Tier 2 trials, with programme goal setting, setting of graded tasks and instruction of how to perform behaviour being amongst the most frequent BCTs. Despite the uncertainty surrounding adherence in some of the included studies, interventions resulted in improvements in aerobic exercise tolerance at eight to 12 weeks (SMD 0.54, 95% CI 0.37 to 0.70; 604 participants, 10 studies; low-quality evidence) versus usual care. At six months, aerobic exercise tolerance was also improved (SMD 0.56, 95% CI 0.39 to 0.72; 591 participants; 7 studies; low-quality evidence). Since the last version of this review, none of the new relevant studies have provided additional information to change the conclusions. We have found some improved understanding of how to encourage previously inactive cancer survivors to achieve international physical activity guidelines. Goal setting, setting of graded tasks and instruction of how to perform behaviour, feature in interventions that meet recommendations targets and report adherence of 75% or more. However, long-term follow-up data are still limited, and the majority of studies are in white women with breast cancer. There are still a considerable number of published studies with numerous and varied issues related to high risk of bias and poor reporting standards. Additionally, the meta-analyses were often graded as consisting of low- to very low-certainty evidence. A very small number of serious adverse effects were reported amongst the studies, providing reassurance exercise is safe for this population.

Plain-language summary: We included only studies that compared an exercise intervention with a usual care comparison or 'waiting list' control. Only studies that included sedentary people over the age of 18 with the same cancer diagnosis were eligible. Participants must have been allocated to exercise or usual care at random. We searched for evidence from research databases from 1946 to May 2018. We included 23 studies involving 1372 participants in total. Evidence suggests that exercise studies that incorporate an element of supervision can help cancer survivors. However, we still have a poor understanding of how to promote exercise long term (over six months). There is some concern that research is not being reported as clearly as it should be. We found that setting goals, graded physical activity tasks and providing instructions on how to perform the exercises could help people to do beneficial amounts of exercise. In addition, we found some evidence that in people who do meet recommended exercise levels, get fitter for up to six months. The main problems that we found regarding the quality of studies in this review included: not knowing how study investigators conducted randomisation for the trials and not knowing whether investigators who were doing trial assessments knew to which group the person they were assessing had been randomly assigned. The quality of the evidence from these studies was found to be low due to the majority of the trials often containing a low number of participants. The main conclusions from this review are that exercise is generally safe for cancer survivors. We have a better understanding of how to encourage cancer survivors to meet current exercise recommendations. However, there is still a lack of evidence of how to encourage exercise in cancer survivors over six months.