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Though surveys show that many women believe birth control pills cause breast cancer, a
new study of over 9,000 women finds that oral contraception does not increase breast
cancer risk in women who have taken "the Pill" in the past. Over 45 million
women have used oral contraceptives at some point in their lives, and an estimated 10
million women between the ages of 15 and 44 take them today. Experts say the study
provides strong evidence that past oral contraceptive use has no significant effect on a
woman’s risk of developing breast cancer.
A previous review of 54 studies found that women who currently or recently used oral
contraceptives face a small increased risk of developing breast cancer, compared to women
who have never taken birth control pills. While experts say it is true that oral
contraception slightly increases breast cancer risk, most women who take the Pill are
young and thus their chances of developing breast cancer are very small. Little research
had been conducted on the risk of breast cancer in older women—in their fifties and
sixties—with a history of oral contraceptive use.
Researchers, led by Polly A. Marchbanks, PhD, of the Division of Reproductive Health at
the Centers for Disease Control and Prevention, decided to investigate whether the use of
oral contraceptives increases the risk of breast cancer later in life, at a time when the
risk of breast cancer is also increased. Their study involved analyzing the health of
4,575 women between the ages of 35 and 64 who had breast cancer and comparing them with
4,682 women of the same age without breast cancer. Approximately four out of five women in
both groups had used oral contraceptives at some point in their lives.
The results of the analysis found no link between past oral contraceptive use and an
increased risk of breast cancer. In other words, women who had used birth control pills in
the past were no more likely to develop breast cancer than women who had never taken the
Pill, even when factors such as age, race, and duration of oral contraceptive use were
considered. The number of women who were currently taking birth control pills in the study
was too small to determine whether they were at a temporarily higher risk of breast
cancer.
The belief that oral contraceptives cause breast cancer stems from the fact that the
Pill contains hormones, including estrogen and/or progesterone (estrogen has been linked
with higher risk of breast cancer in women who take hormone
replacement therapy for five years or more). Birth control pills manufactured prior to
1975 contained significantly higher amount of these hormones, but today’s versions of
the Pill have very low levels of hormones.
In a study reported in the October 11, 2000 issue of the Journal of the American
Medical Association, researchers found that women with a family history of breast
cancer who took oral contraceptives prior to or during 1975 are at a higher risk for
breast cancer than women with similar family histories of breast cancer who did not take
the older versions of birth control pills. The link between breast cancer and oral
contraceptives was found to be strongest among women with five or more cases of breast or ovarian cancer in their families. However, the current
study of over 9,000 women did not find similar results. Researchers of the 2000 study
noted that there was no evidence that oral contraceptives on the market after 1975
increased breast cancer risk.
While oral contraceptives do not cause breast cancer in past users, birth control pills
are associated with a number of side effects for current users. While most side effects
are mild, serious risks include blood clotting, heart attack, stroke,
gallbladder disease, and in rare cases, liver tumors. Smoking greatly increases the risk
of heart attack and stroke among oral contraceptive users. The Pill is also associated
with several beneficial effects in addition to preventing pregnancy. These include a
possible reduction in menstrual
symptoms, reduced risk of acute pelvic inflammatory disease, and a lower risk of ovarian
cancer and endometrial cancer (cancer of the uterine lining).
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