An article recently published by a research group at the Fred Hutchinson Cancer Center in Cancer Research showed that women between the ages of 20 and 44 who used the injectable contraceptive Depo-Provera had an increased risk of developing breast cancer. What does this mean for women who are on or who are considering this form of contraception?
Although Depo-Provera (depo-medroxyprogesterone acetate or DMPA) began to be used in other parts of the world more than 30 years ago, the US. Food and Drug Administration did not approve its use until 1992. Most hormonal birth control options include a combination of estrogen and progesterone. Depo-Provera does not include any estrogen and it is the only progesterone-only option. Women who use this form of birth control receive a Depo-Provera injection every 12 weeks.
Depo-Provera contains the same progestin that was used in the Women’s Health Initiative study, which found women on menopausal hormone therapy (previously known as hormone replacement therapy) had an increased risk of developing breast cancer. This led researchers at the Fred Hutchinson Cancer Center, in Seattle, to question whether young women using Depo-Provera for birth control might also have an increased risk of developing breast cancer.
This was a population-based case-control study. It was not a randomized trial. The researchers compared more than 1000 Seattle-area women, aged 20 to 44, who had been diagnosed with breast cancer with 900 women who were similar to them who had not been diagnosed with the disease. All of the women were asked questions about their health history and their use of birth control.
The study found that women who had recently used Depo-Provera for 12 months or longer had twice the risk of developing invasive breast cancer. The study also found that after women stopped taking Depo-Provera the risk dissipated within months. In addition, no increased risk was seen women who had used the contraceptive for less than a year.
When the FDA first approved Depo-Provera, there were concerns raised about potential cancer risks seen in laboratory animals. A study published in the American Journal of Epidemiology in 2000 did not find an increased risk, which seemed reassuring. This new study means we have more to learn.
The National Cancer Institute estimates that for a woman between the ages of 30 and 39, the risk of developing breast cancer is .43 percent (1 in 233). If this risk is doubled, it’s still low. Also, because this was a case-control study, it can only be said to show a correlation. It does not prove that the Depo-Provera caused the breast cancer.
It is possible that the women who chose Depo-Provera for their form of birth control had other risk factors that contributed to their increased breast cancer risk. Or doctors may have thought that it was safer to put women with a family history of breast cancer on a progestin, rather than estrogen and a progestin. Or this birth control option might have been more favored by women who have never had children, which also increases breast cancer risk. Or women who used Depo-Provera might have had other risk factors that we have yet to identify.
Even so, we should not ignore these findings. This risk also needs to be put in the context of the black box warning that the FDA requested be added to the Depo-Provera label in 2004. This warning was the result of studies that showed that Depo-Provera could significantly decrease bone mineral density; that the bone loss increased the longer women were on the contraceptive; and that this bone loss might not be fully reversible.
The bone density findings were an early alert that Depo-Provera might not be the best choice of birth control for younger women. This new study confirms that. According to it manufacturers, Depo-Provera is not meant to be used as a long-term birth control method (longer than two years). This recent study suggests that increased breast cancer risk may occur after a year. Given that there are numerous other options available, I think it would make sense for younger women to seek out another type of birth control than Depo-Provera.