Breast Cancer Risk May Be Linked to Injectable Contraceptive Use

Christopher I. Li, MD, PhD

Young women who have recently used depo-medroxyprogesterone acetate (DMPA) for at least 1 year have more than twice the risk of invasive breast cancer as young women who do not report recent use of the injectable contraceptive, according to the results of a population-based, case-control study.

Christopher I. Li, MD, PhD, research associate professor in the Department of Epidemiology at the Fred Hutchinson Cancer Research Center in Seattle, Washington, and associates examined the association between DMPA use and breast cancer risk. DMPA contains the same progestin as the menopausal hormone therapy regimen that was shown to increase breast cancer risk among postmenopausal women in the Women’s Health Initiative clinical trials.

Li et al’s study included 1028 women aged 20 to 44 years who had been diagnosed with a primary invasive breast cancer between June 2004 and June 2010 with no prior history of in situ or invasive breast cancer and 919 age-matched controls without a history of breast cancer. Overall, about 10% of participants reported DMPA use.

Earlier case-control studies that were conducted mostly in less industrialized countries consistently found that recent DMPA use was associated with a 1.5- to 1.65-fold increased risk of breast cancer, the authors pointed out. However, more studies on the relationship between DMPA use and breast cancer incidence are needed because earlier reports have included few DMPA users younger than age 45, and none has examined risk stratified by breast cancer subtype. Also, it is not known whether the results could be applied to other populations in more developed countries, which have different breast cancer incidence rates, demographics, and reproductive patterns.

The results showed that DMPA use within the past 5 years for 12 months or more was associated with a 2.2-fold (95% CI, 1.2-4.2) increased risk of invasive breast cancer. The association was maintained regardless of tumor stage, size, hormone receptor expression, or histological subtype.

No increased risk of breast cancer was observed among women who had last used DMPA more than 5 years ago or among women who had recently used DMPA for less than 12 months.

“

...our findings emphasize the importance of identifying the potential risks associated with specific forms of contraceptives given the number of available alternatives.”

—Christopher I. Li, MD, PhD

Li and colleagues said that their research is the first large-scale US study specifically undertaken to assess the relationship between DMPA use and breast cancer risk. They said that their findings are similar to the earlier studies examining recency of DMPA use and breast cancer risk despite significant differences in the study populations.

The investigators also noted that while the study’s case-control design may introduce the potential for recall bias, DMPA is a “unique exposure” because it is administered as an injection and used for a limited time. Recall is thus not likely to be a problem in the study population of young adults.

Finally, the authors pointed out that although breast cancer is uncommon among premenopausal women and the increased risk of breast cancer linked to DMPA use is no longer present after treatment is stopped, “...our findings emphasize the importance of identifying the potential risks associated with specific forms of contraceptives given the number of available alternatives.”

Li CI, Beaber EF, Tang MT, Porter PL, Daling JR, Malone KE. Effect of depo-medroxyprogesterone acetate on breast cancer risk among women 20-44 years of age. Cancer Res. 2012;72(8):2028-2035.