By: Madeline Ellis
Published: Wednesday, 14 October 2009
The placenta is an unborn baby’s lifeline. Attached to the inside of the uterus and connected to the fetus by the umbilical cord, the placenta works as a trading post between the mother’s and the baby’s blood supply. Oxygen and nutrients in the mother’s blood pass across the placenta to the fetus, and metabolic wastes and carbon dioxide from the fetus cross in the other direction. The placenta also helps protect the baby from infections and potentially harmful substances, but it’s not a foolproof filter. Other substances, such as alcohol, drugs, and cigarette smoke can also cross the placenta, with effects including congenital disorders, drug addiction, and fetal alcohol syndrome in the newborn. And scientists have long suspected that cancer can cross the placental barrier and spread from the mother to her unborn child, but have had no proof—until now.
Researchers at the Institute of Cancer Research, a college of the University of London, working with colleagues in Japan, studied the case of a 28-year-old Japanese woman who gave birth to an apparently healthy baby girl after a normal, uneventful pregnancy. A month later, the mother developed vaginal bleeding and was diagnosed with acute lymphoblastic leukemia. She began chemotherapy but developed encephalitis and died 19 days later. The baby showed no signs of illness until she was 11 months old when she was taken to the hospital with a swollen right cheek. Tests revealed she had a tumor in her jaw and the cancer had spread to her lungs.
By comparing DNA from the mother’s bone marrow to that of the baby, the researchers were able to determine that the cancer cells of both mother and child shared the same mutated gene, called BCR-ABL1, but the baby had not inherited the gene. Subsequent testing of a neonatal blood sample taken from the baby confirmed that the cancer had spread before birth.
So how could this have happened? Normally, if the cells crossed the placental barrier, the baby’s immune system would have recognized them as foreign invaders and destroyed them, which is why mother-to-child cancer transmission is so rare. But in this case, the baby’s tumor cells were missing a vital piece of DNA that plays a key role in immune system function. Without this, the cancer cells were able to pass through undetected.
“It appears that in this and, we presume, other cases of mother-to-offspring cancer, the maternal cancer cells did cross the placenta into the developing fetus and succeeded in implanting because they were invisible to the immune system,” said lead researcher Professor Mel Greaves. “We are pleased to have resolved this longstanding puzzle. But we stress that such mother to offspring transfer of cancer is exceedingly rare and the chances of any pregnant woman with cancer passing it on to her child are remote.”
Records dating back to 1866 include 17 cases where a mother and infant appeared to share the same cancer, usually leukemia or melanoma. And while the most likely explanation was that it spread to the infants during pregnancy, other scenarios were theoretically possible. “People have believed that this has been the case for some time. This is really crossing the T’s, dotting the I’s and showing that that’s really the case,” said William H. Chambers, scientific program director at the American Cancer Society.
Dr. David Grant, scientific director at Leukaemia Research, which partially funded the study, said “the important message is that leukemia cells can be destroyed by the immune system.” Knowing this will help scientists find ways to harness the power of the immune system to first cure and then protect patients from leukemia, he said.
The report is published in the October 12 online edition of the Proceedings of the National Academy of Sciences.