Brussels, 25 Apr 2005
The world's largest study into the causes of childhood leukaemia has revealed that although most cases have their origins before birth, a strong immune system, developed in response to common infections experienced in infancy, can ward off leukaemia in susceptible children.
The findings were published in the British Medical Journal by the UK Childhood Cancer Study, based on a 15-year study of almost 12,000 children. The project looked at immunological pathways, exposures to household levels of background radiation (ionising and electromagnetic), parental smoking and occupation, breast-feeding and neo-natal vitamin K administration, as well as a range of factors occurring during pregnancy and shortly after birth.
'The most plausible explanation now seems to be a challenge to the child's immune system, quite possibly involving common infections, which cause the cancerous blood cells to emerge,' explained Sir Walter Bodmer, Chairman of the Leukaemia Research Fund's Medical.
'It is clear that perceived risk factors such as living near sources of electromagnetic fields or natural radiation like radon are not principal causes, if at all, of leukaemia in children;' added Mel Greaves of the Institute of Cancer Research.
In the UK, leukaemia accounts for a third of all cancers in children below the age of 15 with 500 cases diagnosed every year. Although treated with aggressive chemotherapy, 80 per cent of those affected survive.
According to Professor Greaves, two biological events are necessary for leukaemia to develop. The first one is a genetic defect that occurs in the womb, followed by a 'second hit' that precipitates the disease.
About one in 20 foetuses are affected by this chromosomal mutation due to the natural stress of foetal development. However, only one child in 2,000 would develop leukaemia following the second corruption of the genes in early childhood.
The study found that those children who encountered more infections in early life appeared to be better protected from the illness. The immune system needs to be properly 'set up' by exposure to infection to allow it to function normally. Those babies who were not so primed were more likely to suffer the second mutation, which appears to affect 1 in 100 of those who experienced the first one.
The timing or pattern of infection was 'by far the most likely trigger,' stated the study, which found that the greatest reduction in risk (of more than 52 per cent) was seen in children who attended formal day care on a regular basis (once a week) during the first three months of life. To read the full study, please visit: http:///bmj.bmjjournals.com/cgi/rapidpdf/ bmj.38428.521042.8Fv1