A concern that I often get has to do with stem cells causing cancer or making cancer worse. Not all stem cells are created equal, and if you use the wrong kind of stem cells, then yes, they can be dangerous!
Here is the short of it: embryonic stem cells (which are illegal in the United States) are pluripotent cells which means that they can become any tissue. If you put them in a tumor, they cause the tumor to grow.
Stem cells from donated human umbilical cord are multipotent, meaning they can only become a handful of types of cells. Stem cells from human umbilical cord blood have actually been shown to reduce tumors!
For clarity, I want to emphasize that we do not treat cancer.