Injectable Contraceptive is Linked to Increased Risk of Breast Cancer

A large-scale study of US women between the ages of 20 and 44 shows that using the injectable contraceptive, depot medroxyprogesterone acetate (DMPA), is associated with a two-fold increase in the risk of invasive breast cancer when the contraceptive is used for at least one year. The 1,028 woman population-based case-control study is published in Cancer Research.[1]

The injectable contraceptive depot medroxyprogesterone acetate is associated with an increase in the risk of invasive breast cancer

All women were from the Seattle-Puget Sound area and had been diagnosed with breast cancer between 2004 and 2010. Serving as the control group were 919 age-matched women who had no history of breast cancer.

Discontinuation of DMPA resulted in decreased risk of breast cancer within months of stopping exposure to the contraceptive. The authors also found that using DMPA for less than one year did not result in an increased breast cancer risk.

“It is important to acknowledge that breast cancer is a rare disease among young women and that the study showed no increased risk of breast cancer among either former users of DMPA or short term users of DMPA,” said Christopher I. Li, MD, PhD, breast cancer epidemiologist at the Fred Hutchinson Cancer Research Center, and lead author of the study.

DMPA contains the same type of progestin that was linked to increased breast cancer in the Women's Health Initiative trial of menopausal hormone therapy. The current study is the first to assess the link between DMPA and breast cancer risk in premenopausal women

Medroxyprogesterone acetate, the progestin in DMPA, is not used in any oral contraceptive in the United States.

DMPA was approved by the US Food and Drug Administration in 1992-its utilization has steadily increased in the United States and throughout the world. In the study, about 11% of women in the control group, those with no prior breast cancer history, had ever used DMPA, a figure that reflects the national data for contraceptive use.

“There were a series of published studies primarily in the late 1980s and early 1990s in developing countries (Costa Rica, Kenya, Mexico, Thailand) that showed an increased risk of breast cancer among DMPA users,” explains Dr. Li. According to Dr. Li, younger women who have not yet had children predominantly use DMPA in the United States while in other countries the contraceptive is used to prevent further pregnancies. Because pregnancy “confers lifelong protection against breast cancer,” the study authors wanted to specifically assess the effect of DMPA on breast cancer risk in the US population.

“This study points to the potential importance of use of exogenous progestins on breast cancer risk,” said Dr. Li. Dr. Li and colleagues are currently studying the impact of different progestins on breast cancer risk. He also hopes to validate the current DMPA findings in a different population.

The research was funded by the National Cancer Institute and the Department of Defense Breast Cancer Research Program.

Reference

1. Li CI, Beaber EF, Tang MT, et al. Effect of depo-medroxyprogesterone acetate on breast cancer risk among women 20-44 years of age. Cancer Res. 2012 Feb 27. [Epub ahead of print]