Exposure to germs could prevent childhood leukaemia

In a major new analysis, Professor Mel Greaves, one of Britain’s leading scientists, has revealed for the first time the most likely cause of most cases of childhood leukaemia – babies not being exposed to enough microbes.

This means that that the disease may be preventable.

Professor Greaves from the Institute of Cancer Research has assessed the most comprehensive body of evidence ever collected on acute lymphoblastic leukaemia (ALL) – the most common type of childhood cancer, with a risk of developing it around one in 2,000.

Professor Greaves, who has spent more than 40 years researching childhood leukaemia, said there has been huge progress in understanding the disease and its treatment, so that today around 90 per cent of cases are cured, ‘But it has always struck me that something big was missing, a gap in our knowledge – why or how otherwise healthy children develop leukaemia and whether this cancer is preventable.

‘This body of research is a culmination of decades of work, and at last provides a credible explanation for how the major type of childhood leukaemia develops.’

Professor Greaves said there were two steps to the disease. The first one occurs when babies are in the womb and a mutation occurs that is ‘probably a developmental accident’, which predisposes children to leukaemia. However, only about about 1 per cent of children born with this genetic change go on to develop the disease, which is believed to be triggered by infection.

This is primarily in children who experienced 'clean' childhoods in the first year of life, without much interaction with other infants and children.

Professor Greaves said it was the lack of infection in early life that was the problem. The immune system has evolved to fight infections and natural infections in the first few weeks and months of life ‘prime’ the immune system.

‘The research strongly suggests that ALL has a clear biological cause, and is triggered by a variety of infections in predisposed children whose immune systems have not been properly primed,’ he said.

Researchers have found that early exposure to infection in infancy such as daycare attendance and breast feeding can protect against ALL, most probably by priming the immune system.

Professor Greaves added, ‘I hope this research will have a real impact on the lives of children. The most important implication is that most cases of childhood leukaemia are likely to be preventable.

‘It might be done in the same way that is currently under consideration for autoimmune disease or allergies – perhaps with simple and safe interventions to expose infants to a variety of common and harmless “bugs”.’

His idea is that giving children safe bacteria, for example in a yoghurt drink, will help train their immune system.

This will require further research.

Professor Greaves emphasiseD two caveats. Firstly, while patterns of exposure to common infections appear to be critical, the risk of childhood leukaemia, like that of most common cancers, is also influenced by inherited genetic susceptibility and chance.

Secondly, infection as a cause applies to ALL specifically – other rarer types including infant leukaemia and acute myeloid leukaemia probably have different causal mechanisms.

The study is not about blaming parents for being too hygienic. 

For parents who are worried about the risk of childhood leukaemia, Professor Greaves advised them not to be ‘over-zealous’ about hygiene and that children should mix with other children, particularly older children. He also advised breastfeeding for three- to six months.

The research also busts some persistent myths about the causes of leukaemia, he added, ‘such as the damaging but unsubstantiated claims that the disease is commonly caused by exposure to electro-magnetic waves or pollution’.

The research is published in Nature Reviews Cancer.