Neuroproblem,
I searched 'cancer caused by stem cells' and found multiple articles on the theory that ONE'S OWN stem cells drive cancer growth and development, but none on re-introduced stem cells definitively causing cancer. Here is one such article, which also explains the second, less controversial theory of cancer growth:
http://m.eurostemcell.org/de/cancer
One should always amass all the knowledge, not just scan the headlines - 'A Little Learning is a Dangerous Thing'
Dave.
PS. If you read the News report in MrsD's Post you will see that, even here, it is the retrovirus delivery system causing risk - not the stem cells.