In general, one single mutation won’t give you cancer. You need some mutations on specific genes to develop it. Some of this mutations may come with the gene set you inherited from your parents, and all your body cells get this mutation. Other mutations develop during your lifetime by different reasons, but this mutations are not present on every cell your body have, but only on some of them. Everyday you get mutations on your DNA, but most of the cells that get these mutations get eliminated by the immune system. The problem is when you get the set of mutations needed for a cell to divide uncontrollably, and the immune system does not detect this. Cancer cells are more susceptibles to certain treatments that regular cells, so you can use these treatments to eliminate them. If you eliminate all cancer cells, you are cancer free, if not, you might get cancer again. People that inherit mutations from their parent genes, are also more susceptible to get cancer again, as they need fewer other mutations in their cells to develop it.