In cancer and medical terms Ned is short for No Existing Disease.
When you hear NED as a cancer patient that is good news as you have no existing disease and sometimes means that the cancer has been cured.
Cancer can usually be cured depending on the cancer and how far progressed it is.
Cancer is not always a death sentence and many people have gone through chemotherapy and had the cancer cured and lived a long life.
So just because you or someone has cancer it doesn't mean that you will die as long as you can get treatment soon enough.
Still there's no guarantee that the cancer will be cured but sometimes cancer can be cured.