Mayo Clinic scientists have found that women with a strong family history of breast cancer who had ever taken oral contraceptives, particularly those introduced prior to 1975, may have a heightened risk of breast cancer.

"If there is a risk associated with current formulations, we probably don't have the data to detect it," said Thomas Sellers, Ph.D., Mayo Clinic Cancer Center epidemiologist and senior investigator of this study. "What our data suggest is that it is early formulations with high doses of estrogen and progestins that pose a risk, not later ones. More importantly, these results don't apply for women at average risk for breast cancer, who should not interpret the study as reason to change their contraceptive practices."

The study, published in the Oct. 11, 2000, issue of Journal of the American Medical Association, found that the risk of breast cancer is 3.3 times greater for breast cancer patients' sisters and daughters who had ever used oral contraceptives compared to those with similar risk who had never used oral contraceptives.

This did not apply to nieces, granddaughters or women who married into the family, who only had a 1.2-fold greater risk of breast cancer with pill usage.

In families in which five or more blood relatives had been diagnosed with breast or ovarian cancer, the risk was even greater. In those families, sisters and daughters of the breast cancer patients were 11.4 times more likely to develop breast cancer if they had ever taken oral contraceptives.

The elevated risk for first-degree relatives (sisters, daughters) of breast cancer patients was particularly evident for women who had used oral contraceptives introduced prior to 1975, when the formulations were more likely to contain higher doses of estrogen and progestins.

The study could not make statistically significant conclusions about sisters and daughters of breast cancer patients who had used more recent formulations of oral contraceptives containing lower doses of estrogen and progestins, due to the small number of women in the study who had taken them.

"We knew that oral contraceptive use is weakly associated with breast cancer risk in the general population, but the association among women with a familial predisposition to the disease was less clear," said Dr. Sellers. "This new study gives us more information for that population."

Oral contraceptive use by women with a family history of breast cancer is an issue due to the ongoing controversy regarding its risks and benefits.

SOURCES: "Oral Contraceptive and Breast Cancer Linked," Mayo Clinic, October 12, 2000.