Physical activity is becoming increasingly acknowledged as an integral component of in the multidisciplinary management of cancer patients. Intensive inquiry in this area is likely to increase further over the next decade; however, cancer-specific, evidence-based risk assessment and recommendations for physical activity are not available. A systematic literature review was performed of all studies conducting an exercise training intervention and (or) any form of objective exercise test among adults diagnosed with cancer. Studies were assessed according to evaluation criteria developed by a panel of experts. A total of 118 studies involving 5529 patients were deemed eligible. Overall, the results suggest that exercise training and maximal and submaximal exercise testing are relatively safe procedures with a total nonlife-threatening adverse event rate of <2%. There was only 1 exercise training-related death. However, the quality of exercise testing methodology and data reporting is less than optimal. Thus, whether the low incidence of events reflects the true safety of exercise training and exercise testing in cancer patients or less than optimal methodology and (or) data reporting remains to be determined. Evidence-based absolute and relative contraindications to physical activity and exercise training and testing are provided as well as probing decision-trees to optimize the adoption and safety of physical activity in persons diagnosed with cancer.