A UK researcher believes science has now identified what can cause the most common type of cancer in children.
Acute lymphoblastic leukaemia affects one in 2,000 children before they turn 16.
Prof Mel Greaves of the Institute of Cancer Research thinks it starts with a mutation picked up in the womb and an immune system not exposed to enough microbes early in life.
Priming infants to cope with germs might prevent the disease, he says.
The type of blood cancer is more common in advanced, affluent societies, suggesting something about our modern lives might be causing the disease.
There have been wild claims linking power cables, electromagnetic waves and chemicals to the cancer.
That has been dismissed in this work published in Nature Reviews Cancer.
Instead, Prof Greaves believes there are three stages to the disease.
The first is a seemingly unstoppable genetic mutation that happens inside the womb.
The next is a failure to train the immune system in the first year of life.
Coming into contact with microbes is essential for the immune system to learn how to react, but modern society is cleaner than it’s ever been.
Without this lesson, infections later in childhood, such as flu, can cause an immune system malfunction, further genetic abnormalities and cancer.
This “unified theory” of leukaemia was not the result of a single study.
Prof Greaves compiled more than 30 years of studies.
He said: “The research strongly suggests that acute lymphoblastic leukaemia has a clear biological cause and is triggered by a variety of infections in predisposed children whose immune systems have not been properly primed.”
Evidence that helped build the case included:
- An outbreak of swine flu in Milan that led to seven children getting leukaemia
- Studies showing children who went to nursery or had older siblings, which expose them to bacteria, had lower rates of leukaemia
- Breastfeeding – which promotes good bacteria in the gut – protects against leukaemia
- Lower rates in children born vaginally than by caesarean section, which transfers fewer microbes.
- Animals bred completely free of microbes developed leukaemia when exposed to an infection.
Prof Greaves added: “The most important implication is that most cases of childhood leukaemia are likely to be preventable.”
This could include giving children a safe cocktail of bacteria – such as in a yoghurt drink – that will help train their immune system.
This idea will still take further research.
Prof Greaves said parents should “in no way” be blamed for children developing leukaemia, but could “be less fussy about common or trivial infections and encourage social contact with other and older children”.
Dr Alasdair Rankin, the director of research at the blood cancer charity Bloodwise, said: “We urge parents not to be alarmed by this study.
“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.”
This study is part of a massive shift taking place in medicine.
To date our relationship with microbes has largely been one of warfare and yet more than half the cells in our body are microbes.
Recognising their important role on our health and wellbeing is revolutionising the understanding of diseases from allergies to Parkinson’s and depression and now leukaemia.
Prof Charles Swanton, Cancer Research UK’s chief clinician, said: “This research sheds light on how a form of childhood blood cancer might develop, implicating a complex combination of genetics and early exposure to germs, dirt and illness. But it’s important to emphasise that less than one per cent of children who have the genetic predisposition described in this review, go on to develop acute lymphoblastic leukaemia.
“Childhood leukaemia is rare and it’s currently not known what or if there is anything that can be done to prevent it by either medical professionals or parents. We want to assure any parents of a child who has or has had leukaemia, that there’s nothing that we know of that could have been done to prevent their illness.”