A sad story has led to the confirmation of a long-standing hypothesis: in very, very rare cases, a pregnant woman’s cancer cells can sneak through the placenta, evade the developing foetus’ immune system and proliferate in the child.

Since 1866 there have been some 17 documented cases (including the present study) of a baby developing the same cancer as its mother, suggesting that the mother’s cancer cells had metastasized to the developing foetus. This speculation had strong support — for example, three infant boys who developed leukaemia like their moms’ had bone marrow cells with two X chromosomes — but had never been backed by good old genetic evidence. One reason for doubt was that the mother’s cancerous cells, even if they had slipped through the placenta, should have been destroyed by the foetus’ immune system.

Researchers from Japan and the UK have finally demonstrated that mother-to-fetus metastasis can indeed happen, and published their findings online 12 October in PNAS. They focused on a baby who developed a tumour at the age of 11 months. The father then revealed that the mother had been diagnosed with leukaemia a month after giving birth to the child and had died.

The authors found that cancer cells from the mother and the child had the same mutation in the oncogene BCR-ABL1 — but that this mutation hadn’t been inherited, indicating that the cell had passed to the foetus during the pregnancy.

The baby’s immune system didn’t catch the intruder because the cancer cells, the authors found, had deleted the key regions that would have alerted the infant to their foreign status (the mother’s alleles for human leukocyte antigen (HLA), which is the major histocompatibility complex in humans).

An “expert view” from the Guardian notes that the findings are also “further evidence…that cancers are generated more often than we think. It is quite likely that all of us generate small cancers all the time and they are eliminated by the body’s immune system”.

The baby, now about two and a half years old, has been in “complete remission” for 18 months.

More coverage

Passing cancer from mother to baby – LA Times

Mother can pass on cancer in womb – BBC

Scientists prove cancer can be passed on in the womb – Guardian

Mother’s Cancer Can Pass to Fetus – Health Day

Image: Flickr/ZacharyTirrell