Seeds of childhood leukaemia may be sown before birth

The origins of childhood leukaemia may lie in the womb. Jeremy Laurance, Health Editor, examines research suggesting that substances, such as alcohol, to which the foetus is exposed may be a cause of the commonest childhood cancer.

Examination of blood samples taken from children suffering from leukaemia which were compared with blood taken at birth have revealed that the same cancer cells were present when the children were born.

The discovery, by scientists from the Institute of Cancer Research in London, confirms what has long been suspected: that childhood leukaemia starts in the womb.

Professor Mel Greaves and his colleagues, whose findings are published in the US journal Proceedings of the National Academy of Sciences, say they apply to only one type of acute lymphoblastic leukaemia, associated with an abnormal gene, which accounts for one in 20 cases of childhood cancer. However, they say the technique they have developed can be used to trace the origin of other childhood leukaemias.

Professor Greaves said: "It made sense to start with a leukaemia with a convenient molecular marker. It confirms what we suspected. The hints are there that in general there may be a foetal start [for all childhood leukaemias]."

Most cases of childhood leukaemia develop between the ages of two and six, but infant leukaemia begins between six months and one year of age. In these cases it appears that what happens in the womb is enough to cause the disease.

In older children the researchers believe there is an exposure in the womb which makes the child vulnerable but which is not sufficient on its own to start the disease. Later, a "second hit" such as an infection triggers the disease. "It is like a bomb waiting to go off," Professor Greaves said.

A large US epidemiological study has linked drinking in pregnancy with infant leukaemia. But other substances also have a similar effect, including benzene, a constituent of petrol, antibiotics and other medicines.

"There is a list of potential villains," Professor Greaves said. "A lot of women are exposed to them and the disease is rare. That is the way cancer is - it strikes at random. I don't want to worry women who have had a couple of drinks in pregnancy."