decatenation G2 checkpoint
Stem cells lack the decatenation G2 checkpoint that preserves genetic stability. Cells that fail to disentangle chromatids prior to mitosis are prone to the types of chromosomal aberrations that are observed in cancer cells. Ex vivo expansion of stem cells might have the unintended consequence of encouraging malignant progression.
References
Kaufmann WK. Dangerous entanglements. Trends Mol Med. 2006 Jun;12(6):235-7. PMID: #16631407#