US researchers believe that children who are exposed to infection early and often may have a reduced chance of developing acute lymphoblastic leukaemia (ALL) because their immune system is stimulated to tackle infection at an early age.
Scientists think that childhood leukaemia could be caused by a rare immune response to common infections. Delaying a child’s exposure to infection may result in an underdeveloped immune system that produces cancerous cells in response to the barrage of infections a child faces later in life.
Scientists from the Northern California Childhood Leukaemia Study looked at nursery attendance as an indicator of a child’s exposure to common infections.
They analysed 140 children, aged 1-14 years, who were diagnosed between 1995 and 1999 with ALL – a type of leukaemia that results from the accumulation of abnormal white blood cells in the body.
These were compared to a group of children randomly selected from the California birth registry. Detailed data on nursery attendance was collected through questionnaires and interviews with the child’s guardian.
Researchers carried out statistical analyses to compare the two groups to see if there was a relationship between nursery attendance and this childhood leukaemia.
They found that extensive contact with other children in a nursery setting is associated with a reduced risk of ALL. Starting nursery at a younger age, attending for a longer duration and having contact with a high number of children all contributed to a reduced risk of the disease.
Professor Patricia Buffler, principal investigator of the Northern California Childhood Leukaemia Study, says: “As well as attending nursery there are many ways in which the immune system can receive developmental stimulation, such as vaccination and exposure to siblings and friends. Our study contributes to the idea that isolation from common infections can increase the risk of childhood leukaemia.”
Researchers think that delaying a child’s exposure to infections may mean the immune system does not fully mature until the child is older.
When a child with an underdeveloped immune system is eventually exposed to infection he may respond abnormally by producing defective white blood cells that do not fight the infection but build up and may result in leukaemia.
Scientists believe that some children are born with an increased risk of ALL and this, combined with delayed exposure to infection, may lead to the production of defective white blood cells.
Study author Dr Xiaomei Ma says: “The results are from the first phase of an ongoing study. We anticipate that later studies will confirm the association between delayed exposure to infection and childhood leukaemia and eventually lead to effective prevention strategies.”
Professor Buffler says: “While our results strongly support the importance of the timing of infections in the development of childhood leukaemia, we are not able to distinguish whether a particular infection or a number of common infections are involved.”
Sir Paul Nurse, Interim Chief Executive of Cancer Research UK, says: “This research adds to the increasing evidence that infections play a role in some cancers, the nature of which is still unknown.
“Further investigation into exposure to infection with larger numbers of children should help us to identify the role of the immune system in childhood leukaemia and may lead to new ways to prevent the disease. Cancer Research UK is currently funding the UK National Childhood Cancer Study which is looking at the link between infections and leukaemia in over a thousand children.”
Leukaemia accounts for 32% of childhood cancer cases.
ALL is the most common type of childhood leukaemia, the 5-year survival rate for the disease is around 80%.