Children may face cancer even before they leave their mother's womb, an extremely rare scenario but a legitimate risk according to a case study of a Japanese woman and her baby daughter who developed leukemia.

By using advanced genetic fingerprinting techniques, British researchers determined the baby's leukemia cells had developed in the mother and that both patients shared the very same mutated cancer genes. Also, this genetic detective work proved that the baby couldn't have developed leukemia on her own because she didn't inherit these genes from her mom.

So why didn't the infant's immune system ward off cancer cells on its own? The leukemia cells lacked bits of DNA that would've given them their own unique genetic identity, thus the infant's immune system didn't recognize them as a foreign and harmful invader. This lack of recognition allowed the leukemia cells to migrate through the mother's placenta to her child's bloodstream.

Before you start worrying about the health of your baby or grandchild, here's some perspective: There have been only 17 recorded cases (typically melanoma or leukemia) in which a mother and baby shared the same cancer.

Proceedings of the National Academy of Sciences, Vol. 106, No. 42, pp. 17882-17885, October 20, 2009

BBC News October 12, 2009

WebMD October 12, 2009