Contraceptive pills, currently taken by more than 100 million women worldwide, should eventually prevent at least 30,000 cases of ovarian cancer each year, a new report has found.
In fact, since their introduction nearly 50 years ago, oral contraceptives are estimated to have prevented 200,000 ovarian cancers and 100,000 deaths from the disease, concludes the Collaborative Group on Epidemiological Studies of Ovarian Cancer.
The team, which includes researchers from the U.S. National Cancer Institute, published their findings earlier this year in The Lancet.
A key finding: that oral contraceptives' anti-cancer benefit lingers years, even decades after women stop taking them. That's crucial, the researchers say, because a woman's risk of ovarian cancer rises with age.
The findings stem from an exhaustive meta-analysis of 45 epidemiological studies conducted across 21 countries. More than 110,000 women were included in the study, including over 23,000 women with ovarian cancer and 87,303 controls. About 31 percent of women with ovarian cancer had taken some form of the Pill, compared to about 37 percent of controls. Women took an oral contraceptive for an average of between 4 to 5 years.
Overall, women who had ever taken an oral contraceptive were 27 percent less prone to develop ovarian cancer compared to those who had not, the researchers found. The longer the drugs were used, the greater the decline in ovarian cancer risk: about a 20 percent drop for every 5 years a woman took the drug.
And while the Pill's protective effect did subside in the years after a woman ceased taking an oral contraceptive, some protection lingered. For example, the average woman's ovarian cancer risk fell by 29 percent in the first 10 years after she stopped taking the Pill, the study found. But 10 to 19 years after ceasing oral contraceptives her risk was still 19 percent below that of women of similar age who had never taken the drug, and 20 to 29 years out her risk for ovarian cancer remained 15 percent less than that of never-users.
Oral contraceptives also seemed to shield women from almost all forms of ovarian malignancy, including epithelial and nonepithelial tumors, with the possible exception of mucinous ovarian cancer (about 12 percent of the cancers encountered in the study).
Finally, even though the dose of estrogen used in oral contraceptives has decreased dramatically since the 1960s, the time-frame in which women took the drug had no impact on her risk for ovarian cancer, the study found.
Overall, the findings are unprecedented and "set a new standard in prevention for a deadly cancer," The Lancet's editors wrote at the time. They also "have important health implications," they added.
Still, concerns remain. In a commentary, Drs. Eduardo Franco and Eliane Duarte-Franco of McGill University, Montreal, point to the potential side effects of oral contraceptive use, which include blood clots, heart disease. migraine and liver disease.
According to the experts, this means that although the new study does provide "unequivocal good news" on the link between oral contraceptives and ovarian cancer, "women and their health-care providers are once again at a balancing act of judging risks versus benefits."