Help please? what is the difference between cancer going into remission and it no longer existing?

Can be tricky: A cancer is in complete remission when it's not detectable by physical exam, labs, or scans. In some cases, the cancer is gone for good (cured). In other cases, it's still present in microscopic form and thus undetectable. Those are the ones that "come back" months or years later. They don't come back, they were never gone. Only time can sometimes help tell one from the other.