That's one way of looking at the glass half empty.
If half of people get rid of cancer for 1 year that is still outstanding - ESPECIALLY if the majority of those remain cancer free for quite some time after.
The most obvious, naive approach is banking blood & marrow prior to treatment. However, there's a need to clear metastatic cells (CTCs) or train the immune system to find and kill them so that it doesn't reintroduce CTCs upon retransfusion.
If half of people get rid of cancer for 1 year that is still outstanding - ESPECIALLY if the majority of those remain cancer free for quite some time after.