Background <p>Prehabilitation exercise programs implemented between diagnosis and treatment aim to increase functional reserves, reduce perioperative risks, and accelerate recovery.</p> Objective <p>What is the evidence for exercise-based prehabilitation across different tumor entities, and what is known about its safety and benefits?</p> Materials and methods <p>A narrative overview of current study findings is presented.</p> Results <p>Overall, the evidence base is highly heterogeneous with respect to the observed endpoints, study quality, and results. The strongest evidence exists for lung cancer, showing fewer postoperative complications and a&#xa0;shorter length of hospital stay. In urologic tumors, gains are seen primarily in cardiorespiratory fitness and continence, particularly through pelvic floor training in prostate cancer, whereas effects on complications and length of stay are inconsistent. In colorectal cancer, the limited study base suggests improvements in functional capacity, while clinical endpoints show heterogeneous results. In breast cancer, short-term improvements in range of motion and reductions in pain are observed with arm function training. In pancreatic cancer prior to autologous stem cell transplantation and in ophthalmic oncology, there are early indications of improvements in function, activity, and symptom burden.</p> Conclusion <p>Prehabilitation exercise programs are safe and feasible and overall improve physical fitness and functional capacity, with consistent clinical benefits in lung cancer. For other entities, the effects on complications and length of stay are heterogeneous. Priorities appear to be an early start; standardized entity-specific protocols; and, where possible, integration into established care pathways such as structured enhanced recovery after surgery (ERAS)programs.</p>