WEDNESDAY, Dec. 4, 2002 (HealthDayNews) -- Women who have one of the breast cancer genes and take oral contraceptives for five or more years increase their risk of getting early-onset breast cancer, a new study finds.
Researchers looked at the history of birth control pill use in 2,600 women who had mutations in either the BRCA1 or BRCA2 gene, the so-called cancer susceptibility genes. Half of them had developed breast cancer and half had not.
Women with BRCA1 mutations -- but not BRCA 2 -- who used oral contraceptives for five or more years had a 33 percent increase in breast cancer risk compared with BRCA1 carriers who had never used the pill, says study author Dr. Steven A. Narod, a professor and chairman of breast cancer research at the University of Toronto. The research appears in today's issue of the Journal of the National Cancer Institute.
Narod's team also found an elevated risk in those BRCA1 carriers who used the pill before age 30 and who first used oral contraceptives before 1975, when typical doses were higher than in more recent formulations. The longer they used the pill, the higher the risk.
The average age of diagnosis for the women with BRCA1 gene mutations who got breast cancer was 38.6.
Narod puts the elevated risk in perspective this way: In the general population, women have a 9 percent lifetime risk of breast cancer. "Women who are BRCA1 carriers and do not take the pill ever have about a 60 percent lifetime chance of breast cancer," he says. "Women who are BRCA1 carriers and do take the pill for five years have an 80 percent chance. That's my interpretation of our findings."
To incur the increased risk, he adds, they had to begin taking it before age 25.
Women who carry the genes face tough decisions about oral contraceptive use. Research suggests long-term use of the pill is associated with a modest increase in the risk of early-onset breast cancer even in the general population, but oral contraceptives are also found to be protective against ovarian cancer risk, which has also been found to be elevated among those with the breast cancer mutation genes.
The study, Narod says, might help women who have the susceptibility genes make better decisions about contraceptive use. "I would say, if women are over 25, I would recommend they take the pill for five years, which will decrease their ovarian cancer risk by half and not increase their breast cancer risk."
Other experts praise the study and say it will give them something solid to point to when they are asked about the best course of action for BRCA1 and BRCA2 carriers.
"It's a very large study, and that makes the information more applicable," says Monica Alvarado, a certified genetic counselor at the University of Southern California/Norris Comprehensive Cancer Center in Los Angeles. The women were recruited from 52 genetic testing centers in 11 countries. "Prior to this, we were able to tell women [with the gene mutation] that taking the birth control pill reduces ovarian cancer risk but we didn't know what it meant for breast cancer risk. All we could say was there was a suspicion [that it increased risk]."
"We always have to be careful [about making recommendations] based on one study," Alvarado says. "But it's the first time we have any real data from a large study to present to our patients."
Leslie Bernstein, an epidemiologist and professor of preventive medicine at the University of Southern California Keck School of Medicine, calls the study a critical paper. "It's what we would have predicted based on other [smaller] studies, including one we did," she says.
"It's a very well-done study," adds Bernstein, who has studied the association between physical activity and cancer reduction risk for several years. Like Alvarado, she is reluctant to make recommendations based on one study. But she says the new research should provide useful information to women who have the BRCA1 mutation in making contraceptive and other life choices.
What To Do
The National Cancer Institute has information on the genetics and the treatment of breast cancer.
