Childhood leukemia may be triggered by germs, could be prevented, study suggests

According to his review, acute lymphoblastic leukemia (ALL), which is the most common type of childhood cancer, is likely caused by a combination of genetic mutations developed while babies are still in the womb, plus an infection with an unknown bacterium or virus.

"It has always struck me that something big was missing, a gap in our knowledge - why or how otherwise healthy children develop leukemia and whether this cancer is preventable," Greaves, who has been studying ALL for more than 40 years, told Sky News. "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."

The most important implication is that most cases of childhood leukemia are likely to be preventable.

"It might be done in the same way that is currently under consideration for autoimmune disease or allergies - perhaps with simple and safe interventions to expose infants to a variety of common and harmless bugs," he suggested.

According to a report published by the Centers for Disease Control and Prevention (CDC) last year, ALL is the most common cancer among children and adolescents in the United States. The form of leukemia accounts for 20 percent of all cancer cases in people under age 20, with more than 3,000 new cases reported in the country every year.

Greaves' findings suggest that something as simple as exposing children with the first stage mutation to benign microbes may be enough to protect them from developing ALL. If this is the case, thousands of families across the country and around the world could potentially be spared the emotional heartache of a child's leukemia diagnosis.

"The problem is not infection – the problem is lack of infection," Greaves said, according to The Independent.

Previous studies have shown that attending day care, where kids are exposed to bacteria and viruses from others, and breastfeeding both appear to protect children from developing ALL. This is likely a result of the priming effect these activities have on a child's immune system early on.

Although Greaves' review suggests the research is both novel and compelling, some experts point out that his conclusions are not entirely new, "but rather an expansion of concepts that have been considered for many years," Dr. Amelia Langston, a leukemia and stem cell transplant specialist at Emory University's Winship Cancer Institute told The Atlanta Journal-Constitution.

"It happens that we now have the molecular tools to begin to sort out how it all might work, and he incorporates these new data into what amounts to an evolving model," Langston said, adding that "some of the fine details that are proposed [in the review] remain speculative."
"But the point is, they generate testable hypotheses that may lead us closer to an ability to prevent some forms of ALL," she said.

Langston also said many details would need to be worked out before a new strategy for prevention or treatment could be developed. However, the existing data suggests socializing children at an early age is "likely on balance to be a positive thing for the child."

She said this early priming is beneficial for "many reasons," but primarily to help children develop healthy immune systems.

Further laboratory studies are needed to better understand the cause of ALL, according to Langston. But Greaves’ theory does provide a path forward for researchers.

"This will involve both study of patients and animal studies looking at the immune machinery at a very fine level," she said. "The hope would be that if we can fully understand the molecular pathways at work we may be able to tip the balance away from leukemogenesis."

But Langston carries serious doubt that "any single strategy will eradicate this form of ALL."