Aerobic Fitness or Muscle Mass Training to Improve Colorectal Cancer Outcome

First-line treatment of metastatic colorectal cancer (mCRC) generally includes the chemotherapies fluoropyrimidines in combination with oxaliplatin and/or irinotecan, known as doublet or triplet chemotherapy. A previous study showed that over 40% of patients with metastatic colorectal cancer required dose modifications (including dose reductions, treatment delays or discontinuation) within the first three months of palliative treatment, and around 30% was admitted to hospital due to chemotherapy-related toxicity. Toxicity-induced dose modifications and hospitalization may reduce benefit of treatment. In patients with metastatic colorectal cancer, reductions in muscle mass and lower physical activity levels (\<9 metabolic equivalent of task hours/week) were found to be associated with more dose-limiting toxicity and shorter (progression-free) survival. However, the causality and underlying mechanisms linking physical activity and exercise to cancer outcome have not been elucidated. The immune system (by increased infiltration of activated natural killer cells into the tumour) might play a role as was shown in studies with rodents. In addition, studies among patients showed that exercise may counteract a variety of treatment toxicities (e.g. neutropenia, neuropathy, gastrointestinal side effects, fatigue), but optimal exercise type and dose are unknown. In addition to the above-mentioned biophysiological effects by which exercise may prevent dose modifications, several studies demonstrated the positive effects of exercise during cancer treatment on quality of life. A recent study on patients' perceptions indicated that exercise helped patients to better cope with cancer treatments, as it gave them psychological strength (i.e. empowerment and resilience) next to physical strength. The investigators hypothesize that exercise reduces treatment-related toxicity and thereby reduces chemotherapy dose modifications and improves progression free survival. randomised controlled trials are the gold standard for ascertaining treatment efficacy. Studying differences in effects on chemotherapy dose modifications between different exercise programs requires a multi-arm randomised controlled trial. Due to complex logistics and high costs, the conduct of a traditional adequately powered multi-arm exercise trial is difficult with available patients and resources. Therefore, a Bayesian adaptive flexible multi-arm multi-stage design will be used which allows for a number of interim analyses after which a treatment arm can be dropped early if it falls outside the pre-defined futility/efficacy boundaries. This reduces patients' exposure to suboptimal interventions and increases trial efficiency. This study aims to examine whether: 1. Exercise prevents chemotherapy dose modifications via reduced toxicity and enhanced psychological strength, and which exercise program yields largest benefits. 2. Exercise improves immune function (e.g. functionality of natural killer cells). 3. Benefits of exercise on dose modifications and immune function improves progression-free survival.