Just because there’s no known sure cure doesn’t mean there are no treatments for cancer. After all there are no out and out cures for the vast majority of diseases that exist, only treatments to help your immune system fight it off or to slow the growth so your immune system can catch up. Cancer is even trickier because it’s not something from outside your body that we can attack it’s literally your own body cells gone rogue because something inside them broke. Anything we could give that would kill the cancer cells would kill your normal cells to and you need those to stay alive.
Some people beat cancer because it is detected early enough that we can cut it out before it gets anywhere important then heal over time. Others because we can hit it with radiation until the cancer cells get so broken they can’t reproduce which is the thing that makes them dangerous. Some it’s because the immune system manages to get the upper hand because of one of the former two treatments and kill off the cancer cells. Sometimes it is even sheer old fashioned luck where something inside the cancer gets copied wrong taking away its ability to spread forcing it into remission.