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Breast cancer genes and the pill reduce cancer risk

Scott Gottlieb, New York

The regular use of oral contraceptives seems to halve the chance of developing ovarian cancer among women who inherit BRCA1 and BRCA2, two faulty genes that put them at high risk for the disease.

Doctors have known for years that oral contraceptives reduce the risk of ovarian cancer by as much as half among women in general. The new study examined whether those benefits extend to women whose risk resulted from inheriting BRCA1 and BRCA2. While the risk of ovarian cancer among women in general is less than 2%, women with BRCA1 have as much as a 45% chance of developing ovarian cancer in their lifetimes. The risk is 25% among women with BRCA2.

The findings were based on a case-control study of 207 women with ovarian cancer resulting from defective BRCA1 or BRCA2, and 161 of their sisters as controls (New England Journal of Medicine 1998;339:424-8). The controls were enrolled regardless of whether they had either mutation. Lifetime histories of oral contraceptive use were obtained by interview or by written questionnaire and were compared between patients and control women, after adjustments for year of birth and parity.

For women carrying either of the two faulty genes, the risk of developing ovarian cancer decreased with increasing use of oral contraception, and use for six or more years was associated with a 60% reduction in risk. Those who had used oral contraceptives any time in the past had an overall 50% lower risk of ovarian cancer.

The same genetic defects are also responsible for an increased risk of breast cancer, and in some studies, oral contraceptives seem to be independently responsible for increasing the risk of breast cancer, perhaps by 10-20%. Not all studies have confirmed this.

Dr Steven Narod of Women's College Hospital in Toronto, the lead researcher behind the current study, said that his research turned up no sign that oral contraceptives significantly increased the chance of breast cancer in women with the gene defects but that the possibility remains.

Dr Narod's group also warned that different oral contraceptives contain different combinations of hormones, and their findings do not show if one hormone mixture is better than others at preventing ovarian cancer.