Question: If we don't have a cure for cancer what stops it because so people are diagnosed with cancer and get "cured" and don't have it anymore but then in a few months get it again. So my question is how do we make sure someone doesn't have it.
This is a complex question! One way for the cancer to return would be if not all of it was removed in the first place (say if the person has surgery). The second way is that the treatment stopped too soon (chemotherapy or radiotherapy) so not all cancer cells were killed off and third, new cancerous cells could form. So it would be very difficult to know you have gotten out every last cancerous cell, especially those that are the very early stages of disease.