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The incidence of leukaemia in children in England and Wales rose by 20% between the early 1970s and the end of the century, new research shows, an increase of 4% every five years.
The incidence of childhood leukaemia rose from 38.3 per million person years in 1971-5 to 46.1 in 1996-2000, found the study, in the British Journal of Cancer (doi: 10.1038/sj.bjc.6603946). The results also show that throughout the 20th century the incidence of the disease and mortality were at least 15% higher in boys than in girls.
The authors, from the London School of Hygiene and Tropical Medicine, say that the increase cannot readily be explained by a number of theories, including changes in cancer registration. “We are forced to conclude that the increase in incidence is largely real,” they say.
Leukaemia is the commonest cancer in children aged under 14 years. Each year it is diagnosed in some 400 children in England and Wales, of whom around 100 die. Four in five cases of leukaemia in children are acute lymphoblastic leukaemia, while almost all the others are acute myeloid leukaemia.
The authors examined all the available data on trends in incidence of and mortality from childhood leukaemia in England and Wales for most of the 20th century.
The average five yearly increase in incidence over the period 1971-2000 was significant in all age groups, but the overall increase was much larger among children aged under 5 years (46% in infants under 1 year; 24% in children aged 1–4) than in older children (12-15%).
The authors say that five year survival has improved markedly, from less than 5% in the early 1960s to almost 80% by the end of the 1990s.
Although the cause of childhood leukaemia remains unknown, they say, a number of explanations have been suggested for the rising incidence.
One theory is that that some kind of leukaemic exposure may have developed in the early part of the 20th century, possibly associated with better living standards. The continuing rise in the second half of the century, the report says, points to a real rather than an apparent increase.
Another theory is that in the first few decades of the 20th century a fatal infection, perhaps pneumonia, may have killed many children before their leukaemia became obvious and that the later arrival of antibiotics, which limited such infections, would have led to an apparent rise in incidence.
“Even if fatal infections may have had some impact on ‘masking' leukaemia during the first half of the century, their involvement cannot explain the increase in incidence of childhood leukaemia during 1971–2000,” the authors conclude.