A complete remission occurs when all laboratory and other tests (MRI, etc.) appear to be within reference limits. That, at first, should sound just like the definition of a cure - the absence of the disease. The problem is that no test currently in use has that level of accuracy or sensitivity. Most laboratory tests, for example can not pick up signs of a leukemia if there are less than 1,000,000 malignant cells in the body. So I can't tell if you have 0 malignant cells or 999,999 malignant cells. That's why physicians don't use the word 'cure' until 7 to 10 years later. If, in all that time, no malignancy has been noted, then you just don't have any. If a malignancy did occur in that timeframe, then probably these cells were in such low numbers that they could not be detected.