Anti-cancer effect with "the pill" not permanent

Last Updated: 2007-11-07 16:55:03 -0400 (Reuters Health)

By Scott Baltic

NEW YORK (Reuters Health) - Although the use of oral contraceptive pills has been shown to reduce a woman's risk of ovarian cancer, the protective effect disappears roughly 20 years after a woman has stopped using these drugs.

The finding, reported in the American Journal of Epidemiology, stems from an analysis of data from the U.S. Nurses' Health Study. With 107,900 participants and 28 years of follow-up, it is reportedly the longest forward-looking study of ovarian cancer.

Dr. Shelley Tworoger, from Harvard Medical School in Boston, and colleagues found a 38-percent reduction in the risk of ovarian cancer with at least 10 years of oral contraceptive use. No association was found for women who had used oral contraceptives for 5 years or less.

The study also confirmed that the risk of ovarian cancer continued to fall as the duration of oral contraceptive use increased.

As noted, oral contraceptives did not protect against cancer in women who had not used the drugs in at least 20 years.

The study also looked at possible associations between ovarian cancer and other birth control methods. Tubal ligation seemed to reduce the risk of ovarian cancer, a finding that's consistent with other research, although the underlying biologic reasons are not well understood.

Use of an intrauterine device (IUD), on the other hand, appeared to increase the risk by 76 percent.

"Given that oral contraceptive use is one of the best ways to reduce risk of ovarian cancer, it should be considered a prevention option, particularly for women who are at high risk," Tworoger told Reuters Health. "However, our results highlight the need to find other prevention mechanisms for women who are diagnosed at an older age."

SOURCE: American Journal of Epidemiology, October 15, 2007.