Cancer is caused by bad-luck random cell division creating a bad cell That is only the first necessary step towards cancer. Our bodies have various mechanisms

Cancer is caused by bad-luck random cell division creating a bad cell That is only the first necessary step towards cancer. Our bodies have various mechanisms to kill suspicious cells before they start being a systemic problem. Apoptosis, or the immune system attacking them if they can be recognized. These mechanisms are pretty efficient; in the animal world, animals with really strong immune systems, like bats, very rarely get cancer. And most of our current progress against cancer involves ... very careful stimulation of the immune system against targets specific for that particular patient's tumor. Physical activity can probably influence these anti-cancer mechanisms, as does aging etc.