A report to be published next week in the Journal of the National Cancer Institute, in the US, will say that a study of nearly 2,000 women, half of whom were cancer patients, found an increased risk of 50 per cent.
However, in an accompanying commentary, Professor Lynn Rosenberg, of the Boston University School of Medicine, warns that more information is needed before cause and effect can be established. Other factors could be as important she says.
British experts said yesterday that the link was not properly substantiated and that women who have had abortions should not panic.
Professor Gordon McVie, scientific director of the Cancer Research Campaign, said: 'If women under the age of 18 who have abortions have a raised risk it would follow that they are delaying their first pregnancy.
'It is already well established that later pregnancy increases a woman's risk of breast cancer. This could be a telling factor.
'A 50 per cent increased risk is small. By far the greatest risk of breast cancer is a family history of it. Women who have had abortions should not worry about this but join the national breast cancer screening programme when they are 50.'
Professor McVie also said that since both breast cancer and abortions were common the two groups would overlap, which makes it difficult for researchers to draw conclusions. 'Unless there is a hormonal factor at play I cannot see how it would follow,' he said.
The work was conducted at the Fred Hutchinson Cancer Centre, in Seattle, by Dr Janet Daling. The cases of 845 breast cancer patients and 961 'controls' were studied.
Women under the age of 45 who had a pregnancy terminated earlier in their lives were at a 50 per cent higher risk of tumours than other women in the same age group, who had been pregnant at least once.
This increased risk did not vary by the number of abortions or by the history of a completed pregnancy. But it was greater if the abortion was performed before the age of 18 - particularly after an eight week pregnancy.Reuse content