Exploring the Link Between Injectable Contraception and Breast Cancer
Thirty-five million women worldwide use injectable contraceptives such as Depo-Provera (also known as DMPA) to prevent unwanted pregnancy, and this number is projected to grow. In some regions of the world—for example, sub-Saharan Africa—DMPA is the most widely used modern contraceptive method. DMPA is popular among women for many reasons: it is discreet, affordable, highly effective, and convenient, only requiring a reinjection every 13 weeks. Furthermore, because DMPA only contains progestin and not estrogen, breastfeeding women can use it for postpartum family planning.
Despite its many benefits, the scientific community has raised several concerns about DMPA use. In the past, these concerns have included a loss of bone mineral density among users, though research has demonstrated that this loss is reversed once use is discontinued. This winter, a study published in The Lancet Infectious Diseases suggested an increased risk of HIV infection among women who use DMPA. However, after a careful review of the evidence, the WHO issued a statement in February affirming that women with HIV or at high risk of HIV can safely use hormonal contraceptives to prevent pregnancy but that these women should always use male or female condoms to protect against HIV infection.
For more commentary of the WHO’s statement concerning DMPA, read “WHO Upholds Guidance on Hormonal Contraceptive Use and HIV Risk) by Ruwaida Salem.
Most recently, a study published in the journal Cancer Research in April linking DMPA use with a heightened risk for breast cancer has raised concerns about the method’s safety for young women. Researchers compared 1,028 American women ages 20 to 44 who had been diagnosed with breast cancer with 919 women in the same age group who had never had breast cancer. They found that recent use of DMPA for 12 or more months was associated with a 2.2-fold increased risk of invasive breast cancer. These findings confirm the results of previous studies in Costa Rica, New Zealand, Kenya, Mexico, Thailand, and South Africa, which associated recent DMPA use with 1.5 to 1.65-fold increased risks of breast cancer. While the new study, like its predecessors, showed that the increased risk evaporated within months after women discontinued use and that women who used DMPA for less than twelve months or who had stopped using it more than a year earlier were not at increased risk of breast cancer, the results have caused many to wonder whether DMPA should still be included in the range of contraceptive options available to young women who wish to prevent pregnancy.
Because breast cancer is so uncommon among young women, there is insufficient data from clinical trials to examine the link between DMPA and breast cancer, and it is not feasible to launch a new clinical trial to pursue this link. Therefore, researchers must rely on observational studies such as this case-control study to try and pinpoint the risks of DMPA use. Because observational studies are susceptible to bias, it is difficult to determine the true strength of the association between DMPA and breast cancer. For example, we do not know whether researchers are seeing a heightened risk of breast cancer among current and very recent DMPA users because DMPA users are under more surveillance and therefore receiving earlier detection of breast cancer or because there is an actual biologic effect of DMPA that accelerates the growth of pre-existing cancerous cells.
Given the rarity of breast cancer among young women, many in the public health community likely feel that the health benefits of making DMPA available to women who wish to prevent pregnancy outweigh the risks. DMPA does not require daily action or action at the time of sexual contact and provides longer-term protection than the pill or barrier methods, yet it is not as long-acting as implants or intrauterine devices (IUDs), to which some women are not ready to commit. These unique characteristics highlight the value of continuing to offer DMPA as a contraceptive option. However, more research is needed on the link between DMPA and breast cancer if the family planning community wishes to continue to credibly promote this injectable to women as a good contraceptive option.