Having a miscarriage does not increase a woman's risk of breast cancer at any age, according to one of the largest ever studies on the link between reproductive factors and the disease.

But the research, which involved 91,000 French women, confirms what scientists had suspected-that women who have children late or start their periods early are at increased risk. Of the women in the study, 1,718 were eventually diagnosed with breast cancer over the time period.

Writing in the British Journal of Cancer, Dr. Francoise Clavel-Chapelon and colleagues tracked women over a ten-year period, sending them detailed questionnaires and recording both reproductive factors and whether or not they developed breast cancer. Premenopausal and postmenopausal women were studied separately, in order to find out whether reproductive factors affected the two groups differently.

Previous research on miscarriage had produced conflicting results, with some smaller studies suggesting that it might increase the risk of the disease and a recent paper also linking abortion with increased risk. But the new, large-scale research found no evidence that women with a history of miscarriage were at higher risk of breast cancer in either the premenopausal or postmenopausal group.

"In the past, the fear of breast cancer has added to the anxiety already felt by women who have miscarried. I'm very glad to be able to allay those fears," said Clavel-Chapelon.

The researchers also found that women who had their first child relatively late did seem to be at increased risk of the disease, with the increase appearing to be greatest in the premenopausal group.

Compared with those who gave birth before the age of 22, women who had their first child in their thirties were 63 per cent more likely to develop breast cancer before menopause and 35 per cent more likely to get the disease afterwards.

One of the study's most intriguing findings was that the later a girl started her periods, the lower her chance of developing breast cancer later in life. A woman whose periods had started at the age of 15 was at only two thirds the risk of premenopausal breast cancer compared with someone whose periods had started at 11, with a decrease of 7 per cent for each year that periods were delayed.

SOURCE:
British Journal of Cancer, February 12, 2002; 86:723-727