But another expert cautioned that the study did have its limits.
Dr. Freya Schnabel, director of breast surgery at NYU Clinical Cancer Center in New York City, noted that the women in the study who seemed at highest risk of developing breast cancer while on Depo-Provera were those with a family history of the disease or women who had never had children (another known risk factor).
Furthermore, she said, "the study did not include information about all breast cancer risk factors in the participants, and this is a real limitation of the analysis which could impact on the results. Also, the mechanism by which the progesterone would increase risk only in current users is not clear."
According to Schnabel, all of this means that "more detailed studies are needed to clarify the relationship between this contraceptive method and risk of breast cancer."
The research was funded by the U.S. National Cancer Institute and the Department of Defense Breast Cancer Research Program.
Planned Parenthood has more about the birth control shot.
-- Robert Preidt
SOURCES: Elizabeth Poynor, M.D., Ph.D., Lenox Hill Hospital, New York City; Freya Schnabel, M.D., director of breast surgery, NYU Clinical Cancer Center, New York City; Fred Hutchinson Cancer Research Center, news release, April 4, 2012
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