Recent use of an injectable form of progestin-only birth control for a year or more doubles the risk of breast cancer in young women, according to a large-scale US-based study.
“While DMPA [depomedroxyprogesterone acetate] is widely used by women throughout the world, there are limited data on the association between DMPA and breast cancer incidence,” said study leader and breast cancer epidemiologist Christopher I. Li, MD, PhD, of Fred Hutchinson Cancer Research Center. “Our study adds to the body of knowledge from international studies conducted in a diverse group of countries – Kenya, New Zealand, Thailand, Mexico and Costa Rica – which have shown that one of the risks associated with DMPA use may be an increased risk of breast cancer,” he said.
Li and colleagues studied 1028 Seattle-area women between the ages 20 and 44 who had been diagnosed with breast cancer and, for comparison purposes, 919 age-matched controls without a history of breast cancer. About 10% of these participants reported using DMPA, which, according to Li, is consistent with rates of use throughout the nation. Use of the injectable contraceptive was about 5% higher among nonwhite women in the study.
Study results showed that DMPA use within 5 years for 12 months or longer was linked to a 2.2-fold increased risk of invasive breast cancer. Within months after contraceptive use was discontinued, the risk appeared to dissipate. The researchers did not discover any increased risk of breast cancer in women who used the contraceptive for less than a year or who had stopped using it more than a year earlier.
The authors wrote, “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.”
“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,” Li said.
The results of the study are published online ahead of the April 15 print issue of Cancer Research.
Source: Fred Hutchinson Cancer Research Center.