A leading scientist has identified the likely cause of childhood leukaemia – and said most cases could be prevented.
Professor Mel Greaves of the Institute of Cancer Research said a combination of a genetic mutation while babies are still in the womb, followed by an infection with an unknown bacteria or virus, is the most likely cause of the blood cancer.
Acute lymphoblastic leukaemia (ALL) is the most common type of childhood cancer, with 500 cases diagnosed in the UK each year. Around 90% are cured.
Professor Greaves, who has been studying childhood leukaemia for more than 40 years, debunked theories that radiation, high voltage electricity cables or chemicals caused leukaemia.
He said: "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."
In a review of previous studies, published in the journal Nature Reviews Cancer, he said most cases of the disease are caused by two crucial steps.
The first occurs in the womb, when a random genetic mutation predisposes the baby to leukaemia. But only 1% of children born with the alteration go on to develop the disease.
The second is caused by exposure to one or more common infections, particularly if children have had 'clean' upbringings, with little exposure to bugs from siblings or other social interactions.
The finding suggests that exposing children with the first stage mutation to benign microbes early in life could be enough to protect them from developing leukaemia.
"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," Prof Greaves said.
"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."
Dr Alasdair Rankin, director of research at blood cancer charity Bloodwise, said: "Current treatments for childhood leukaemia are not always successful, and even when they are, can have severe short and long-term side effects, so research to find kinder treatments is very important.
"If we could stop this type of leukaemia from happening in the first place it would be enormously exciting, but many more questions still need to be answered.
"We urge parents not to be alarmed by this study – childhood leukaemia is very rare and only around one in 2,000 children will develop it.
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"While developing a strong immune system early in life may slightly further reduce risk, there is nothing that can be currently done to definitively prevent childhood leukaemia.
"As noted by this study, other factors influence its development – including pure chance."