Most cases of childhood leukaemia are either predetermined before birth or are triggered by infections very early in life, according to research released today.
The 15-year-long United Kingdom childhood cancer study (UKCCS), published on bmj.com today, says common infections might be setting off an abnormal immune response as part of a "double hit" that leads to leukaemia.
Leukaemia experts examining the survey at a meeting this week said the timing of exposure to common infections was critically important and that children were also predisposed by chromosomal difference in cells that develop before birth.
Prof Mel Greaves, from the Institute of Cancer Research in London, said around one in 20 children could be affected by the chromosomal differences they had outlined but only one in 2,000 youngsters would develop leukaemia.
He also said further research into the infections that can trigger leukaemia could eventually lead to the development of a vaccine for the disease.
The researchers ruled out links between power lines and natural radiation and leukaemia. Prof Eve Roman, director of the epidemiology and genetics unit of the Leukaemia Research Fund at York University, said the study had found "absolutely no link between measurements of electromagnetic fields in homes and leukaemia and childhood cancers".
However, other research published on bmj.com contradicts the findings on exposure to infection. It says children who are regularly cared for in day-care centres in the first three months of their life are 52% less likely to develop leukaemia than youngsters who are not.
Children exposed to informal day care, such as that provided by friends and family, had a 38% drop in their risk of suffering acute lymphoblastic leukaemia, while those who had some social activity, but not day care, had a 27% lower risk.
"Our results provide further support that social activity with other infants and children during the first few months of life protects against subsequent risk," the researchers said.
The UKCCS gathered information on 3,838 children diagnosed with cancer, including 1,737 with leukaemia, and compared them with 7,629 youngsters without cancer. The researchers looked at the children's exposure to background radiation, parental smoking, breast-feeding and vitamin K, which is given to babies soon after birth.
