Twins may be at reduced risk of children's cancer
Twins may have a lower than average risk of developing childhood cancer, Cancer Research UK scientists in Oxford believe.
Preliminary studies of 13,000 twins born in or around Oxfordshire suggest that they have a 20 per cent lower chance of developing the disease than the population as a whole.
A larger-scale international study to attempt to confirm the finding and explore possible reasons for a decrease in risk is now being launched, the charity announces.
Scientists examined data from the Oxford Record Linkage Study, which includes all birth registrations in the area between 1963 and 1989. They cross-referenced their data with the National Registry of Childhood Tumours in order to identify twins with cancer.
Among 13,000 twins, researchers identified a total of 15 cases of children's cancer - four fewer than for an average population sample of that size and age. The difference was not on its own statistically significant, but when they combined the data with previously published studies, they found a significant 15-20 per cent reduction in risk.
The team will now be analysing other data sets, including a much larger one taken from children born within the Utah Morman community in the United States, to see if they can confirm their findings and attempt to measure more precisely the size of the risk reduction.
Fifty thousand babies born as twins, together with non-twin siblings, and 50,000 singleton comparison babies will be studied.
Lead researcher Dr Mike Murphy, of the Cancer Research UK General Practice Research Group in Oxford, says: "Because children's cancer and twinning are both comparatively rare, really large studies are needed to investigate the relationship.
"We were surprised and intrigued by the results of our initial research, which suggested that twins are at lower than normal risk of children's cancer. It will now be exciting to take that work to a much larger population sample, in order to see if we can confirm the findings, and to investigate whether there is a familial influence.
"Of course the really interesting question is why twins should be at reduced risk. Answering that could give us some important information about the factors that contribute to childhood cancer, which in turn could help us with prevention or treatment."
Scientists are unsure about why being a twin should bring a lower cancer risk. Twin pregnancies differ from singleton pregnancies in a variety of ways in terms of the overall foetal and placental mass and associated hormone levels.
Dr Murphy adds: "One possibility is that it is simply a result of twins being smaller than single new-borns; another that they have a greater tendency to die of something else, so the cancer doesn't get a chance to appear."
Sir Paul Nurse, Chief Executive of Cancer Research UK, says: "We're doing better than ever at treating childhood cancer, but prevention would be an even better option, and for that we need to know exactly how and why cancer develops in children.
"Our researchers in Oxford are shedding light on the contribution of prenatal factors to cancer risk and their new study of US data should bring important results."
Notes to Editor
December 2002 was Children's Cancer Awareness Month which aimed to highlight the need for continuing research into the treatment and prevention of the disease.
Cancer Research UK spends over three million pounds each year on research into children's cancers.
From January 2003, Dr Mike Murphy will be the new director of the University of Oxford Childhood Cancer Research Group.
The incidence of children's cancer is approximately one in 1,000. The incidence of twin birth is around one in 100.
Dr Murphy's team have chosen to study a data group taken from children born within the Utah Morman community purely due to the availability of genealogical data from the Church of Jesus Christ of Latter Day Saints.