Cancer

Article date: 2008/01/28
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Summary: Previous studies have shown that taking birth control pills reduces ovarian cancer risk. A comprehensive study published in The Lancet shows just how much.

Oxford University Professor Valerie Beral, along with researchers from the Collaborative Group on Epidemiological Studies of Ovarian Cancer, which includes researchers at the American Cancer Society, analyzed data from 45 studies conducted in the 1960s, '70s, and '80s. They found that the longer a woman took birth control pills, the lower her risk of ovarian cancer.

Why It's Important: Ovarian cancer typically strikes late in life (half of all ovarian cancer cases are found in women over 63), and prognosis is often poor, largely because the disease is usually caught in its later stages. Ovarian cancer symptoms, which include abdominal swelling and digestive problems, are easily confused with other disorders, and there is currently no good screening test available to women.
According to the study, if the current level of oral contraceptive use remains steady, 30,000 cases of ovarian cancer worldwide could be prevented each year. Even better, the protection that comes with the pill seems to start within a year of taking it and increase over time.

What's Already Known: Scientists have known for some time that birth control pills protect against ovarian cancer, and that certain lifestyle factors may affect risk. Age, weight, and a woman's reproductive and family history also appear to play a role in the likelihood a woman might develop ovarian cancer.
However, there's also some data that suggests oral contraceptive use increases the risk of other cancers. Cervical cancer has been linked to long-term birth control pill use, as has breast cancer. (For more information, see "What are the Risk Factors for Cervical Cancer?" and "What are the Risk Factors for Breast Cancer?")
But the picture is complicated. "Oral contraceptives slightly and temporarily increase the risk of breast and cervical cancer. However, the slight increase in breast cancer occurs during and in the 5 years following the use of these contraceptives, and usually at a time and age when risk is very low," said Debbie Saslow, PhD, director of breast and gynecological cancers at the American Cancer Society.

How This Study Was Done: Researchers mined data from 45 studies that included 23,257 women with ovarian cancer and 87,303 without the disease. They determined whether the women had taken birth control pills and for how long.
Scientists then examined the relationship between oral contraceptive use and ovarian cancer diagnosis during the 1960s, 1970s, and 1980s. The amount of estrogen used in birth control pills lessened over the years, and they wanted to see if different estrogen doses had different effects on ovarian cancer risk. They also adjusted for the role of age, ethnicity, education, reproductive history, family cancer history, use of hormone replacement therapy, body mass index, and consumption of tobacco or alcohol, in addition to other factors.