Each five-year interval of oral contraceptive use cuts a woman's ovarian cancer risk by up to 29%. The longer a woman uses the pill, the lower her risk of ovarian cancer, find Valerie Beral, MD, director of the Cancer Research Epidemiology Unit at Oxford University, England, and colleagues.
"We can say the longer women take it, the longer the protection, which lasts 30 years after they stop," Beral tells WebMD. "This does outweigh any other cancer risk from taking the pill. So the net effect is to reduce cancer overall. Women on the pill do not need to worry they are putting themselves at long-term risk of cancer."
It's been known for a long time that oral contraceptives cut a woman's lifetime risk of ovarian cancer. It's also known that the drug increases a woman's risk of breast and cervical cancer while she's on the pill. Now Beral and colleagues have been able to put numbers on these risks.
"In breast and cervical cancer there is increased risk, but these effects disappear and are not persistent after a woman discontinues oral contraceptives," Beral says. "Whereas ovarian cancer protection lasts for decades -- into the ages when this cancer becomes more common for a woman."
Pill's Anticancer Effect 'Definitive'
An astonishing amount of data went into the study. Beral and colleagues combined data from 45 high-quality studies that included detailed data on 23,257 women with ovarian cancer and on 87,303 women without ovarian cancer.
They calculate that over the 50 years oral contraceptives have been on the market, the drugs have prevented at least 200,000 ovarian cancers and prevented 100,000 deaths. Because use of the pill is increasing, they predict that the pill will prevent at least 30,000 cases of ovarian cancer each year for the next several decades.
It's an "unequivocal protective effect," says Eduardo Franco, DrPH, director of the division of cancer epidemiology at Montreal's McGill University. Franco's editorial accompanies the Beral paper in the Jan. 26 issue of The Lancet.
"This study decides once and for all there is a real protective effect against ovarian cancer that is strong and cuts across all demographic groups," Franco tells WebMD.
Over-the-Counter Birth Control Pills?
Another editorial, by the editors of The Lancet, argues that the time has come for "more widespread over-the-counter access to an agent that can not only prevent cancers but also demonstrably save the lives of tens of thousands of women."
Beral says the call for over-the-counter availability of oral contraceptives stems from the high rate of teen pregnancy in the U.K. She does not endorse taking birth control pills solely to prevent ovarian cancer.
"People should take the pill for other reasons than cancer prevention," she says. "But there is a bonus when they do use the pill for these reasons: They will be at reduced risk of cancer."
Franco, too, says it would be unwise for women to take birth control pills just for cancer prevention.
Franco opposes over-the-counter availability of oral contraceptives.
"There are harmful effects from oral contraceptives as well as good ones. It is a balancing act between risks and benefits," he says. "That is why it is a prescription medication. Women who take oral contraceptives should be monitored, and there is advice that goes with prescribing them. It is not a simple matter, so a doctor has to be part of the equation."