Women who take oral contraceptives have a slightly increased risk of developing breast cancer early in life, with the risk being greatest for women who use oral birth control before they have their first child, a new analysis suggests.
Researchers combined the findings from 34 previous studies designed to examine the impact of oral contraceptive use on breast cancer diagnosed before menopause.
Twenty-one of 23 studies that followed women who took oral birth control before having their first child showed an increased risk of early breast cancer.
Based on these studies, the researchers concluded that taking oral contraceptives before a first full-term pregnancy increases premenopausal breast cancer risk by 44 percent, compared with women who have never used oral contraceptives.
The increase in risk was 52 percent among women who took the pill for four years or more before having their first child.
“I think women should know about this risk, and they are not being told,” researcher Chris Kahlenborn, MD, of Altoona Hospital in Altoona, Pa., tells WebMD.
“Anyone who is prescribing oral contraceptives has a duty to tell women that 21 out of 23 studies showed an increased risk.”
Breast cancer is most often diagnosed in women over the age of 50, but cancers that occur in younger women tend to be more aggressive. It is the leading cancer killer among women between the ages of 20 and 59 in the U.S.
Kahlenborn says he conducted the analysis because he believes far too few women know the risks associated with oral contraceptive use.
“As I studied the medical literature, I noticed that a trend appeared,” he says. “Namely, oral contraceptive use prior to first full-term pregnancy seemed to consistently increase the risk of premenopausal breast cancer. Although the trend was apparent, premenopausal women have continued to hear that oral contraceptives are safe.”
The 34 studies chosen for the analysis included women who were premenopausal or younger than 50 whose breast cancers had been diagnosed during or after 1980.
Studies examining breast cancers diagnosed before this were excluded in an attempt to approximate the risk with oral contraceptives as they are currently prescribed.
When all the studies were combined, use of oral birth control was associated with a 19% overall increased risk of breast cancer diagnosed before menopause. But the increase in risk more than doubled among women who took oral contraceptives before a first pregnancy.
Risk Still Small
In an editorial accompanying the study, Mayo Clinic epidemiologist James Cerhan, MD, PhD, points out that though the link between oral contraceptive use and early breast cancer appears real, the risk is still quite small.
Cerhan notes that a previous analysis calculated the risk of excess breast cancers occurring up to 10 years after stopping oral birth control. Researchers concluded that one excess breast cancer could be expected for every 20,000 women who used oral contraceptives from ages 16 to 19 and 4.7 cancers could be expected for every 10,000 women who used them from ages 25 to 29.
According to Cerhan's editorial, there is evidence that oral contraceptive use can reduce a woman’s risk for ovarian and endometrial cancers, and recent studies suggest that it may also protect against colorectal cancer.
He writes that use of oral birth control is also believed to reduce the risk of pelvic inflammatory disease, benign breast disease, ovarian cysts, and other reproductive-related health problems.
Cerhan concludes that if oral contraceptive use early in life increases a woman’s breast cancer risk, other early-life influences probably do, too.
By Salynn Boyles, reviewed by Louise Chang, MD
SOURCES: Kahlenborn, C. Mayo Clinic Proceedings, October 2006; vol 81: pp 1290-1302. Chris Kahlenborn, MD, department of internal medicine, Altoona Hospital, Altoona, Pa. James R. Cerhan, MD, PhD, division of epidemiology, Mayo Clinic College of Medicine, Rochester, Minn. The Lancet, 1996; vol 347: pp 1713-1727.