Injectable contraceptive doubles risk of breast cancer, study shows

(CBS News) An injectable form of birth control doubles breast cancer risk among young women, according to a new study.

The study examined younger women, ages 20 to 44, and confirmed a link between depo-medroxyprogesterone acetate (DMPA) - the main ingredient in the contraceptive sold under the brand name Depo-Provera - and breast cancer risk. The contraceptive shot is usually injected into the buttocks or upper arm once every 3 months, or just under the skin once every 12 to 14 weeks.

Long-term hormone use ups breast cancer risk, even estrogen

The contraceptive contains progestin, the same hormone used in a menopausal therapy that has previously been found to increase risk for breast cancer. But researchers say few studies have examined the link between DMPA and breast cancer risk, and this is the first large scale U.S. study to do so.

The study, led by researchers at the Fred Hutchinson Cancer Research Center in Seattle, is published in the April 15 issue of Cancer Research.

The research involved over 1,000 young women diagnosed with breast cancer. About 10 percent of those women reported using DMPA, which study authors say is consistent with nationwide usage patterns.

What did the results show? Women who had used DMPA for at least one year had a risk for breast cancer 2.2 times greater than those who did not use the injectable birth control. Women who had used DMPA for less than a year or had stopped using it more than a year ago did not have an increased risk, meaning discontinuing use may be effective.

"Although breast cancer is rare among young women and the elevated risk of breast cancer associated with DMPA appears to dissipate after discontinuation of use, our findings emphasize the importance of identifying the potential risks associated with specific forms of contraceptives given the number of available alternatives," the authors wrote in a news release.

Lead author Dr. Christopher Li of Fred Hutchinson Cancer Research Center in Seattle, Wash. said in a statement, "In the United States many women have numerous options for contraception, and so it is important to balance their risks and benefits when making contraceptive choices."

The CDC has more on contraception.