Study Suggests Germ-free Childhood Causes High Leukemia Risk


Germ-free childhoods followed by infections later in life can trigger the onset of childhood leukemia, a new study suggests.

The paper, published Monday in the journal Nature Reviews Cancer, finds that acute lymphoblastic leukemia, the most common type of childhood cancer, is caused by a two-step process.

Acute lymphoblastic leukemia, known as ALL, is a form of blood cancer that is most often diagnosed in children ages zero to 4 years old, though older children and adults can also be diagnosed. It develops quickly, over days or weeks, building up in the blood and spreads to other parts of the body, including the lymph nodes, liver and nervous system. The main form of treatment is chemotherapy.

The first step is a genetic mutation before birth that predisposes a child to the risk of developing this form of leukemia. The second step is exposure to certain infections later in childhood, after clean early childhoods that limited exposure to infections.

More specifically, children who grew up in cleaner households during their first year and interacted less with other children are more likely to develop acute lymphoblastic leukemia, the paper says.

The author, Institute of Cancer Research Professor Mel Greaves, suggests the cancer could be preventable. Greaves reviewed more than 30 years of research, including his own, on the genetics, cell biology, immunology, epidemiology and animal modeling of childhood leukemia and reached this conclusion. Greaves said he had long wondered “why or how otherwise healthy children develop leukaemia and whether this cancer is preventable.”

“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,” he said in a statement. “The research strongly suggests that (this cancer) has a clear biological cause, and is triggered by a variety of infections in predisposed children whose immune systems have not been properly primed.”

The body of research “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,” said Greaves.

Greaves instead believes that when a baby is exposed to infections during its first year, its immune system is strengthened. But later infections, without the initial priming, can trigger leukemia in those with the genetic mutation.

Population studies have found that early exposure to infection in infancy such as day care attendance and breastfeeding can protect against ALL, probably by priming the immune system, according to the study.

Greaves emphasized that infection as a cause applies only to ALL. Other types of leukemia, including infant leukemia and acute myeloid leukemia, probably have different causal mechanisms.

However, other experts warn that more specifics need to be confirmed and emphasize that hygiene and safety are still crucial.

“It’s also important to remember that infections themselves can pose a significant risk for young babies with a developing immune system,” said Cruickshank in a statement. “Parents should not be unduly alarmed by this review.”

The research may be a step toward developing preventative measures. However, Charles Swanton, chief clinician of Cancer Research UK, stressed that the causes and prevention methods are still unconfirmed.

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