Suggestions of a link between abortion and breast cancer have been made for more than a decade and are among the most controversial in medicine. More than 150,000 abortions are carried out each year in Britain and the threat that they could trigger malignant disease is a potent weapon used by the anti-abortion lobby to deter young women from terminating unwanted pregnancies. But the Royal College of Obstetricians and Gynaecologists denies there is evidence of a link.
The study, which will include hundreds of thousands of women worldwide, will be led by Valerie Beral, one of the country's leading epidemiologists, who works at Radcliffe Infirmary, Oxford. Dr Beral conducted the ground- breaking studies of breast cancer and its links with the contraceptive pill and hormone replacement therapy. The abortion study, funded by the Imperial Cancer Research Fund, will be an extension of those.
Life, the anti-abortion organisation, claimed last week that 24 out of 30 recent articles published in medical journals around the world showed a "clear link" between abortion and breast cancer. "The evidence suggests that women who undergo induced abortion are at least 30 per cent more likely to develop breast cancer, perhaps decades afterwards," it said.
It claimed that abortion caused 1,300 deaths a year from breast cancer and that the first 30 years of the 1967 Abortion Act had claimed 40,000 women's lives.
But the Royal College of Obstetricians and Gynaecologists has rejected Life's claims. A meeting of its scientific advisory committee concluded that the data was conflicting and that there was "insufficient evidence to associate breast cancer with induced or spontaneous abortion".
Professor Eric Thomas, chairman of the committee, said: "I would take issue with the conclusion Life drew. The data are much more heterogeneous than they suggest."
Professor Beral said that there was no strong evidence linking abortion to breast cancer but that it was worth examining the data to settle the question.
"There is not a single article that shows without question that there is a link and the best one, by Melbye in Denmark, showed no link," she said.
That study, published in the New England Journal of Medicine, was one of the few "prospective" studies which identified women who had had abortions first and then followed them to see if they later developed breast cancer. Most studies have been retrospective, that is, they identified women with breast cancer and then asked them whether they had an abortion in the past. If that occurred before abortion was made legal the women may have been reluctant to admit it, distorting the results of the studies.
Professor Beral said there had been about 50 unpublished studies, almost twice the number published, which were more likely to show no link because of the tendency of journals to select articles with positive rather than negative findings. This "publication bias", common to all medical journals, tended to skew the perception of the problem.
"We don't know if this is an issue worth talking about but it is worth getting an answer to settle the question so that we don't have to deal with these regular queries," she said.
The main factors influencing breast cancer risk are linked with a woman's reproductive history which in turn affects the levels of the female hormone, oestrogen, to which she is exposed.
Having children protects against breast cancer but the greater the mother's age at the birth of her first child the higher the risk.
The length of a woman's reproductive life is also linked with the disease. The younger the age at menarche (first period) and the older the age at menopause, the higher the risk.
Professor Beral's study of the Pill found it conferred a slightly increased risk of breast cancer for 10 years after stopping use. Users of HRT also have a slightly increased risk but this is almost certainly outweighed by the reduced risk of heart disease.Reuse content