Hormonal contraception is used by women worldwide. Yet the association between its use and the risk of breast cancer continues to be uncertain. Most previous research was conducted when the estrogen dose in estrogen-progestin contraceptives was higher than it is today and before the availability of new types of progestins and new routes of delivery.

The association between the use of currently available hormonal contraceptives and the risk of breast cancer was recently assessed in a nationwide study of Danish women of reproductive age. The study included nearly 1.8 million women between ages 15 and 49 years who hadn't had cancer or venous thromboembolism, or been treated for infertility. They were followed for a mean of 11 years.

A total of 11,517 cases of breast cancer occurred during the study period. The relative risk of breast cancer among current and recent (discontinuation within the past six months) users of any hormonal contraception compared with women who had never used these medications was 1.20. This risk increased with duration of use: from 1.09 with less than one year of use to 1.38 with more than 10. Compared with women who had never used hormonal contraceptives, women who had previously used these agents for five or more years were also at an increased risk for breast cancer, and the increase remained higher for at least five years after discontinuation. Risk estimates were similar regardless of the type of hormonal contraception used.

The absolute difference in breast cancer risk between current and recent users of hormonal contraceptives and women who had never used these agents was 13 cancers per 100,000 person-years-approximately one extra breast cancer diagnosis for every 7,690 women using hormonal contraception for one year. The authors note that the risk should be weighed against hormonal contraception benefits, such as contraceptive efficacy and a potentially reduced risk of ovarian, endometrial, and colorectal cancer.

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