Hank Schmidt, MD, PhD, Assistant Professor of Surgery at The Mount Sinai Hospital
Many historical studies have addressed the question of whether women who use birth control pills, or contraceptive devices such as IUDs that release hormones, face an increased risk of breast cancer. Unfortunately, these studies have failed to reach a consensus.
In fact, doctors and researchers believe many of these studies are limited because they examined older forms of hormonal contraceptives containing different estrogen doses and different progestin medications.
The result: This important question lacks a definitive answer—a critical shortcoming because nearly 10 million American women use oral contraceptives.
A recent analysis from the Danish Sex Hormone Registry Study in The New England Journal of Medicine offers new data in an attempt to answer this question, and many women may want to discuss these findings with their doctor.
The study found a significant increase in risk of breast cancer among women using oral contraceptives. The study included nearly 1.8 million women age 15-49 who were followed, on average, for 10 years. It found 11,517 breast cancers, and a relative risk of 1.2 among users of oral contraceptives—meaning that a woman who uses oral contraceptives was 1.2 times more likely to develop breast cancer compared to women who did not use these contraceptives. Relative risk increased to 1.38 with 10 years of oral contraceptive use.
It is important to put this increased risk into perspective. It translates into 13 additional breast cancers per 100,000 women for the total study group, and two breast cancers per 100,000 women under 35 years of age. Bottom line: This study indicates oral contraceptive use may be a modest risk factor for breast cancer, similar to rates from increased alcohol intake or postmenopausal weight gain.
The study also found that change in breast cancer risk did not seem to be related to the specific type of oral contraceptive used. Women using implanted intrauterine devices (IUDs) releasing progestin also showed similar increased risk. For short-term users, typically those who used these medictions for less than five years, the increased breast cancer risk seemed to rapidly disappear with discontinuation; however, longer-term users, those who used the medications for more than five years, sustained increased risk for at least five years after they stopped using them.
In assessing your own risk, it is also important to remember that hormonal contraceptives have documented benefits, such as a reduction in risk of ovarian cancer and possibly colorectal cancer. Women who are at increased risk of breast cancer from other factors, such as a strong family history of breast cancer, should discuss the risks and benefits of oral contraceptive use with their doctors.
Hank Schmidt, MD, PhD, Assistant Professor of Surgery at The Mount Sinai Hospital and Director of the Cancer Risk Program at the Dubin Breast Center of the Tisch Cancer Institute, is a board certified surgeon specializing in surgical oncology and treating patients with breast cancer.