Preventing cancer that prevents reproduction or hampers offspring survival is a priority for evolution.
Cancer affecting the old is not strongly de-selected for by evolution.
Cancer affecting the old is not strongly de-selected for by evolution.
I also don't subscribe to the theory that individuals have to procreate to boost the survival of their genes. In reality it's a bit more complex than that, and even very old people can and do contribute to the survival of their children or their close relatives.