Stem cells grown in laboratories may pose a cancer risk if put in humans.

Stem cells are capable of changing into different types of adult cells and are being studied for their potential use in the treatment of diseases.  Research performed in Israel and the U.S. raises warning flags about the use of transplanted stem cells in humans.  The researchers examined 66 human and 38 embryonic stem cell samples and found that many of them were genetically abnormal.  The cells contained defects in chromosome number and structure.  Many of the stem cells produced increased amounts of proteins involved in cell division.  The results suggest that the defective stem cells may be more capable of causing tumor formation if transplanted into humans.