Copenhagen, Denmark—While past studies of breast-cancer risk among women using hormonal contraceptives have been conducted, the findings have varied widely, ranging from no increase in risk to a 30% greater likelihood of developing breast cancer. 

A recent report in the New England Journal of Medicine also points out that few studies have focused on combined oral contraceptives containing specific progestins, especially newer products containing desogestrel, gestodene, or drospirenone.

Another concern, which University of Copenhagen–led researchers sought to remedy, was that none of those trials have been large enough to provide useful risk estimates for specific combinations.

“New methods such as the levonorgestrel-releasing intrauterine system, contraceptive patches, vaginal rings, progestin-only implants, and injections now account for almost one third of all hormonal contraceptives used in many countries, including Denmark,” the authors point out. “Concern regarding the progestin content of hormonal contraceptives has arisen because studies have indicated that the addition of progestin appears to increase the risk of breast cancer among postmenopausal women who receive hormone therapy.”

The study team assessed associations between the use of hormonal contraceptives, including birth control pills as well as devices, and the risk of invasive breast cancer in a nationwide prospective cohort study involving all women in Denmark aged between 15 and 49 years who had not had cancer or venous thromboembolism and who had not received treatment for infertility. All of the information—the use of hormonal contraception, breast-cancer diagnoses, and potential confounders—was available in nationwide Danish registries. Among 1.8 million women who were followed on average for 10.9 years, 11,517 cases of breast cancer occurred.

Results indicate that the relative risk of breast cancer among all current and recent users of hormonal contraception was 1.20 (95% confidence interval [CI], 1.14 to 1.26) compared to women who had never used hormonal contraception, increasing from 1.09 (95% CI, 0.96 to 1.23) with less than a year of use of to 1.38 (95% CI, 1.26 to 1.51) with more than a decade of use.

Researchers report that, even after discontinuation of hormonal contraceptives, the risk of breast cancer was still higher among the women who had used hormonal contraceptives for 5 years or more versus women who had not used hormonal contraceptives. Specifically, they add, risk estimates associated with current or recent use of various oral combination (estrogen-progestin) contraceptives ranged between 1.0 and 1.6. The higher risk of breast cancer also was found in women who currently or recently used the progestin-only intrauterine system, compared to those never using hormonal contraceptives (relative risk, 1.21; 95% CI, 1.11 to 1.33).

Overall, the absolute increase in breast cancers diagnosed among current and recent users of any hormonal contraceptive was calculated at 13 (95% CI, 10 to 16) per 100,000 person-years, or approximately one extra breast cancer for every 7,690 women using hormonal contraception for each year, according to the industry-funded study.

“The risk of breast cancer was higher among women who currently or recently used contemporary hormonal contraceptives than among women who had never used hormonal contraceptives, and this risk increased with longer durations of use; however, absolute increases in risk were small,” the study authors emphasize.
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