Contemporary Hormonal Contraception and the Risk of Breast Cancer

Authors: MØrch, L. S. et. al.

Source: NEJM 2017; 377:2228-39

www.nejm.org/doi/full/10.1056/NEJMoa1700732

The use of hormonal contraception has been linked to breast cancer, apparently raising the risk for the disease. It has been suspected for years that this association was due to the estrogen present in the preparations. Current oral products now contain varying amounts of progesterone. Some intrauterine devices are impregnated with variations of progesterone. For postmenopausal women, the progesterone in combined (estrogen and progesterone) hormone replacement therapy is associated with increased breast cancer risk. It is possible that the progesterone in oral and intrauterine contraceptive products increases the risk of breast cancer, as well.

The investigators followed over 1.7 million Danish women in the Danish Sex Hormone Register Study, which was established to evaluate the effects of hormone use on the risks of cancer and cardiovascular disease. Follow up was 17 years. The use of contraceptives and breast cancer diagnoses among the participants were documented.

The relative risk of developing breast cancer was 1.2 times greater among women who used oral hormonal contraception compared to women who had never used it. This risk was essentially the same for women who used the intrauterine devices. The risk grew with increased duration of contraception use. Interestingly, women who used contraception for five or more years had persistently increased risk of breast cancer for at least five years after stopping the medication.

The study does have some weaknesses. Many experts believe that an outcome (breast cancer) can be linked to a specific cause (hormonal contraceptives) only if the relative risk is 2 or greater. A relative risk of 1.2, even if statistically significant, is not high enough to conclude that hormonal contraception increases breast cancer risk.

Also, the ages of the women studied were 15-49 years while the majority of breast cancers are diagnosed after age 50. Among the participants, risk factors for breast cancer, such as personal estrogen exposure (such as age with first period), alcohol consumption and level of physical activity were not recorded. Moreover, family history of breast cancer was only considered if affected relatives were premenopausal at diagnosis.

While this study raises the possibility of increased breast cancer risk with progesterone-containing contraception, the risk appears to be small and there may have been other factors responsible for the development of breast cancer in these women. Women considering such therapy should discuss their individual risks, benefits and health goals with their physician.