Stem cells work to cure cancer by replacing the bone marrow cells that have been destroyed because of cancer or if the bone marrow cells have been destroyed by the chemo that is used to treat and cure cancer.
Stem cells survive much longer than ordinary cells, increasing the chance that they might accumulate genetic mutations.
It might take only a few mutations for one cell to lose control over its self-renewal and growth and become the source of cancer.
Stem Cells are viable for around 25 years in storage.
However they may be viable even longer but the storage of stem cells has not been around all that long to know for sure if they will last longer but they are likely to be viable longer than 25 years.
Stem cells and cord blood banking has been around for at least 25 years and so far stem cells and cord blood has remained viable for those 25 years so far.
So we do know that stem cells and cord blood remain viable for at least 25 years when it's stored properly using cord blood banking.
However since cord blood and stem cell banking have not been around longer than 25 years as of now we cannot know how much longer stem cells and cord blood remain viable.
Hopefully the stem cells and cord blood never need to be used but it's likely that the stem cells and cord blood will remain viable for 30 to 50 years or even longer.
But most people would not be around or want to store cord blood or stem cells longer than 50 or so years anyway.
But at least as of now we know that the cord blood and stem cells are still viable and usable after 25 years of storage.