Childhood leukaemia likely driven by common infections such as flu

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Childhood leukaemia is driven by common childhood infections meeting pre-cancerous cells in the blood, scientists believe.  

Experts at the Institute of Cancer Research (ICR) in London have found babies develop the risk for leukaemia in the womb, but will not go on to develop the disease without a second ‘hit’ from a viral or bacterial infection, such as flu.

The research highlights the importance of allowing infants to socialise with other children early in their lives, to prime their immune systems against infections.

The discovery came by studying pairs of twins, where only one initially developed acute lymphoblastic leukaemia (ALL) – the most common type of the cancer in children.

Identical twins are around 15-25 per cent more likely to go on to develop ALL if their sibling already has the disease, while less than one per cent of non-identical twins or other siblings go on to develop the disease.

Researchers followed the twins for up to 15 years and found the high risk only applies if the identical twins shared a single placenta before birth – which only happens in around 60 per cent of identical twin pairs.

Findings ‘confirm disease can be traced back to womb’

It confirms that the conditions needed to trigger leukaemia first arise in the womb, and even the healthy twin will carry “pre-leukaemia” cells in the blood, which have occurred through a spontaneous developmental error, and passed between the two.

But clinically silent cells will not develop into cancer without a post-birth “hit”, probably from common childhood infections.

Prof Sir Mel Greaves, the founding director of the Centre for Evolution and Cancer and Professor of Cell Biology at The Institute of Cancer Research, London, said: “Our study provides new insights into the origins of childhood acute lymphoblastic leukaemia.

“These new findings confirm that the disease can be traced back to the womb when pre-leukaemia cells spread via the twins’ shared blood supply.

“What remained a mystery until now was why sometimes only one twin is diagnosed with leukaemia.

“We still do not know for certain what leads to the first ‘hit’ of genetic changes in the womb, but we think that the second ‘hit’ of genetic changes is probably triggered by common childhood infections – opening up the possibility of ‘priming’ the immune system in infancy to avoid the development of the disease later on in life.”

Acute lymphoblastic leukaemia is the most common type of childhood cancer, accounting for 80 per cent of leukaemia cases in children.

The team are now focussed on finding the the second infection-driven hit after birth.

Boosting the gut could protect children against disease

They believe that the gut microbiome may be playing a key role in protecting children against developing leukaemia even if they have pre-cancerous cells. Although vaccines have little impact on preventing ALL, boosting the gut in early life may help.

Prof Greaves added: “Risk of ALL is elevated by C-section birth, lack of breast feeding and paucity of social contacts in infancy.

“Conversely, attendance at play groups in infancy is protective. So, to some extent , risk can be modified without medical intervention.”

The findings will also allow doctors to assess the risk of ALL for twins,  firstly by determining whether the twins are identical and sharing a placenta and then by regularly tracking the levels of pre-leukaemia cells in their blood.

Sarah McDonald, the deputy director of research at Blood Cancer UK, who funded the work said: “Understanding the mechanism as to how the cancer develops in identical twins, and why often only one develops leukaemia is an important question to answer.

“It helps us understand both the risk of the other sibling developing leukaemia and provides insight into how leukaemia develops in all children.

“This research shows that in cases where one twin develops leukaemia, and both twins both share a placenta during pregnancy, two events are needed to determine whether the other sibling develops the disease – one before birth and the other after.”

The research was published today in the journal Leukaemia.

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