Oral contraceptives may protect against breast cancer

Mar 22 2005

Women at high genetic risk of breast cancer could reduce their risk of developing the disease at an early age by taking oral contraceptives, a new study has found. The findings contradict previous studies, which suggested oral contraceptive use would increase the risk of developing breast cancer.

Professor John Hopper from the University of Melbourne says the research showed that the lifetime risk of breast cancer for women who have inherited a “high-risk” mutation in the breast cancer gene BRCA1 was reduced from 40-80 per cent to 10-20 per cent if the women used oral contraceptives.

Professor Hopper says, “These findings are important because women who carry a mutation in BRCA1 or BRCA2 (the other known breast cancer-susceptible gene) are also at increased risk of ovarian cancer. It is well known that oral contraceptive use reduces a woman’s risk of ovarian cancer, and our study suggests the same could be true of breast cancer for BRCA1 mutation carriers.”

“If more studies confirm that oral contraceptive use could prevent BRCA1 carriers from both breast and ovarian cancer, it would be possible to offer women with this high genetic cancer risk a safe and easy way to lower their risk.”

“Currently, the only known way to reduce risk in mutation carriers is to surgically remove the breasts or ovaries.”

Professor Hopper, who is Director of the University’s Centre for Genetic Epidemiology, led the international study into the relationship between oral contraceptive use and the incidence of breast cancer. The findings were recently published in the journal Cancer Epidemiology, Biomarkers and Prevention.

“The lifetime risk of breast cancer in Australia, the USA and Canada is around 10 per cent,” Professor Hopper says. “For women who have inherited a “high-risk” mutation in the breast cancer gene, BRCA1, the lifetime risk is 40-80 per cent.”

“We found that this lifetime risk was reduced to 10-20 per cent for those women who used oral contraceptives, much closer to that for women not carrying a mutation.”

Oral contraceptive use did not appear to influence breast cancer risk in women with a mutation in the other known breast cancer-susceptible gene BRCA2. The risk of early-onset breast cancer is greater for women with a BRCA1 mutation than those with a BRCA2 mutation, Professor Hopper says.

The findings contradict previous studies, which suggested oral contraceptive use would increase the risk of developing breast cancer.

“We are confident in our findings because we found the same results in Australia, Canada and the United States, and in women with and without a family history of breast cancer,” Professor Hopper says.

Professor Hopper suggests that one reason the new findings may differ from previous studies is that the dosage and composition of oral contraceptives has changed significantly since the 1970s, when the first studies into the relationship between breast cancer risk and oral contraceptive use were performed. Another is that, unlike other studies, this study sampled women from the general population and used the same questionnaires in all countries.

However, he stresses that more studies are now needed to confirm the present findings.

The research involved collaboration between the University of Melbourne, Cancer Care Ontario, Toronto, Canada and the Northern California Cancer Centre, USA as part of the international Breast Cancer Family Registry funded by the National Institutes of Health (USA).