A review of studies has provided some promising clues on the causes of the most common type of cancer in children, and the researcher behind the work says the disease could even be preventable.

According to the data, acute lymphoblastic leukaemia (ALL) is a combination of a genetic mutation, and then exposure to a common infection – after the child has experienced a 'clean' first year of life.

ALL affects one in 2,000 children, and its rate has been increasing in affluent countries by about 1 percent a year. Even though scientists already knew there were some genetic risk factors, this research gives a solid basis to how the devastating cancer forms.

"I have spent more than 40 years researching childhood leukaemia, and over that time there has been huge progress in our understanding of its biology and its treatment - so that today around 90 per cent of cases are cured," said the review author Mel Greaves, from the Institute of Cancer Research in London.  

"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."

Greaves looked at a large collection of papers to determine how and why this cancer forms.

In the review, he discusses how a genetic change in the womb causes something called a pre-leukaemic clone.

Then, in the first year of life, a lack of exposure of microbes stops the immune system from learning how to deal with biological threats correctly.

Finally, in a small number of cases, a common infection triggers the second mutation, leading to the development of ALL.

"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," said Greaves.

"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."

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

There was a number of evidence points Greaves used in his review including animal studies that show animals that are bred free of microbes develop leukaemia when exposed to an infection.

He also looked at studies that show children who were breastfed, went to nursery, or had older siblings, have lower rates of leukaemia.

Importantly, Greaves believes that with this information, we could even prevent this type of leukaemia from developing at all.

"Most cases of childhood ALL are potentially preventable," he writes.

"A more realistic prospect might be to design a prophylactic vaccine that mimics the protective impact of natural infections in infancy, correcting the deficit in modern societies."

It's important to note that we still need to gather more information about this disease, and this review is probably not the final word on the matter.

"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," explains Alasdair Rankin, from the UK blood cancer charity Bloodwise.

"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."

The research has been published in Nature Reviews Cancer.