Physical exercise interventions and analysis of genetic susceptibility as strategies to prevent chemotherapy-induced toxicity

The number of patients surviving cancer increases. Survivors of cancer often face adverse effects from their treatment, like fatigue and a higher risk of cardiovascular disease. Exercise leads to a better physical fitness and a decrease in cardiovascular diseases and cancer mortality. In this thesis, predictors of adherence to exercise interventions in patients with cancer were investigated. To improve motivation and adherence to exercise interventions, potential pre-existent barriers to participate in these interventions, like limited knowledge or experience of exercise, should be identified and discussed before starting the cancer treatment. This might help to motivate patients with cancer to participate in an exercise intervention during or after cancer treatment. This thesis also investigated the optimal timing of an exercise intervention to improve cardiorespiratory fitness of patients with breast cancer, testicular cancer and colon cancer: during or after chemotherapy. Measured directly after chemotherapy, the patients who exercised during chemotherapy had a better cardiorespiratory fitness, better muscle strength, better quality of life and experienced less fatigue compared to patients who started exercising after completion of chemotherapy. One year after completing the exercise intervention, the difference in these outcomes were diminished. Our findings show that exercise during chemotherapy helps patients to recover faster. Finally, it was investigated which patients with testicular cancer have a genetically increased risk of developing pulmonary and cardiovascular toxicity due to chemotherapy. Screening for genetic predisposition to develop side effects could contribute to personalized cancer treatment and thereby minimizing the risk of developing adverse effects.