According to scientists, childhood leukemia is caused by common childhood infections that encounter precancerous cells in the blood.
Experts from the Institute of Cancer Research (ICR) in London have found that babies develop the risk of leukemia in the womb, but won’t develop the disease without a second ‘hit’ of a viral or bacterial infection, such as influenza.
Research highlights the importance of allowing infants to socialize with other children early in life, to prepare their immune systems against infections.
The discovery came by studying sets of twins, where only one initially developed acute lymphoblastic leukemia (ALL) – the most common type of cancer in children.
Identical twins are about 15-25% more likely to develop ALL if their sibling already has the disease, while less than 1% of non-identical twins or other siblings develop the disease.
The researchers followed the twins for up to 15 years and found the high risk only applied if the identical twins shared a single placenta before birth – which only happens in about 60% of identical twin pairs. .
The results ‘confirm that the disease can be traced back to the uterus’
This confirms that the conditions necessary to trigger leukemia first appear in the womb, and even the healthy twin will carry “pre-leukemic” cells in the blood, which arose through a spontaneous developmental error, and passed between the two.
But clinically silent cells won’t develop into cancer without a postnatal “hit,” likely from common childhood infections.
Professor Sir Mel Greaves, Founding Director of the Center 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 acute lymphoblastic leukemia in child.
“These new findings confirm that the disease can be traced back to the uterus when pre-leukemic 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 don’t know for sure what leads to the first ‘hit’ of genetic changes in the womb, but we think the second ‘hit’ of genetic changes is likely triggered by common childhood infections – opening up the possibility of ‘priming’ the immune system in early childhood to prevent the development of disease later in life.
Acute lymphoblastic leukemia is the most common type of childhood cancer, accounting for 80% of childhood leukemia cases.
The team is now focused on finding the second blow caused by infection after birth.
Stimulating the gut could protect children from disease
They believe the gut microbiome may play a key role in protecting children from developing leukemia, even if they have precancerous cells. Although vaccines have little impact on preventing ALL, stimulating the gut early in life may be helpful.
Prof Greaves added: ‘The risk of ALL is increased by caesarean birth, lack of breastfeeding and lack of social contact in early childhood.
“Conversely, participation in early childhood playgroups is protective. Thus, to some extent, the risk can be modified without medical intervention.
The results will also allow doctors to assess the risk of ALL for twins, first by determining whether the twins are identical and share a placenta, then by regularly monitoring the levels of pre-leukemia cells in their blood.
Sarah McDonald, deputy director of research at Blood Cancer UK, which funded the work, said: “Understanding the mechanism of cancer development in identical twins and why often only one develops leukemia is an important question to be addressed. reply.
“It helps us understand both the risk of the other sibling developing leukemia and provides insight into how leukemia develops in all children.
“This research shows that in cases where one twin develops leukemia and both twins share a placenta during pregnancy, two events are needed to determine whether the other sibling develops the disease – one before birth and one after. .”
The research was published today in the journal Leukaemia.