It’s a sobering statistic, but 1 in 8 women will develop breast cancer. It’s diagnosed more than any other type of cancer and is the second-leading cause of cancer-related deaths for women in the United States.
“Breast cancer is very common and, if caught early, very treatable, but it’s also largely out of our control—a mix of genetic and environmental factors is to blame,” says Melissa Troester, PhD, professor in the Department of Epidemiology and director of the UNC Center for Environmental Health and Susceptibility. “Even so, there are steps each woman can take to reduce her individual risk.”
Here’s what to know.
Uncontrollable Risk Factors for Breast Cancer
It may feel like common sense, but being a woman is the biggest risk factor.
“Ninety-nine percent of breast cancer cases are found in women,” Dr. Troester says. “However, it is important to mention that while it is rare, men can get breast cancer as well.”
Another leading risk factor is age. As a woman gets older, her risk of getting breast cancer increases. Most women who get breast cancer are 50 or older, but younger women get it, too; about 11 percent of new cases of breast cancer in the U.S. are found in women younger than 45.
Family history is another key risk factor that a woman can’t control. If a woman has breast cancer in her family, she’s more at risk for getting it. And if the individual in her family is a first-degree female relative—her sister, mother or daughter—that risk is even higher. About 5 to 10 percent of breast cancers are hereditary, which means they result from a gene mutation you get from a parent.
Risk Factors for Breast Cancer That a Woman Can Control
Controllable risk factors for breast cancer fall primarily into four categories: what you drink, what you weigh, how much you move and whether you smoke.
Research has shown that drinking alcohol increases breast cancer risk, even for women who drink moderately. A 2017 report found that even one small drink a day (10 grams) increased breast cancer risk by 5 percent for premenopausal women and 9 percent for postmenopausal women. Women who drink more heavily—three drinks a day—are 1.5 times likelier than nondrinkers to get breast cancer.
“The increase in risk due to moderate drinking is small, but alcohol is known to affect hormone metabolism and is associated with increases in DNA damage,” Dr. Troester says. “Alcohol is actually associated with increased risk of a number of different kinds of cancers.”
Another risk factor within a woman’s control, at least somewhat, is her weight.
The ways in which fat increases risk are not fully understood. One theory is that the more fat a woman has in her body, the more estrogen her body makes, and estrogen may cause the growth of breast cancer. This risk is significantly higher in women who are postmenopausal. Keeping your body mass index under 25 is a good way to minimize risk. Prevention is the key, because it isn’t clear whether weight loss can reduce risk for a woman who is already obese. The question of weight loss and breast cancer risk is particularly hard to study because women’s weights vary over their lives. However, it’s indisputable that maintaining a healthy weight is best for your overall health.
Of course, it’s easier to maintain a healthy weight with exercise, which carries additional benefits for reducing breast cancer risk. Studies have shown that physically active women have a lower risk of breast cancer than women who do not exercise; the preventive effect appears to be even stronger after menopause. Exercise can lower estrogen levels and boost the body’s immune system, which might help account for its breast cancer-preventing powers.
Finally, women who want to reduce their breast cancer risk—and their risk of lung cancer, heart disease and a host of other potentially fatal illnesses—should quit smoking. Smoking has been shown in some studies to slightly increase breast cancer risk, not just for the smoker but also for others exposed to secondhand smoke. Whether or not it causes breast cancer, smoking is the No. 1 cause of preventable death.
If you’ve heard that oral contraceptives might increase breast cancer risk, that’s true—but it’s complicated. Studies have tied taking the pill to an increased risk of breast and cervical cancers, but also to a reduced risk of endometrial, ovarian and colorectal cancers. A 2017 study from the New England Journal of Medicine concluded that women who currently use or recently used hormonal contraceptives were at higher risk for breast cancer than women who had never used such methods, regardless of today’s modern low-hormone pills. That said, the increase in risk was small.
“Decisions about birth control are complex decisions,” Dr. Troester says. “Women must balance the real risk of an unwanted pregnancy against longer-term and much smaller risks of breast cancer.”
As for other things you may have heard cause breast cancer, from deodorant to underwire bras to trauma to the breast, don’t spend too much time worrying—the data aren’t there to support those theories.
“Studying environmental and personal care product risk factors is complicated because there are many different exposures and lots of different formulations,” Dr. Troester says. “Consumers should educate themselves about ingredients in products they use because many chemicals aren’t well-tested or studied.”
Getting Screened and Advances in Treatment
Women at average risk should start talking to their doctors about breast cancer screening, likely with a mammogram, at age 40. Some women choose to wait until 45 or later to get screened, but 40 is the age to at least start the conversation, Dr. Troester says.
Each woman has a different risk profile, though; for women at higher risk of breast cancer, for example because of family history, mammograms should begin earlier, probably in the 30s. Again, a conversation with your doctor is key.
“Early detection is so important,” Dr. Troester says. “We see a lot of success with treating breast cancer that is detected early.”
In fact, the five-year survival rate for women with stage 0 and stage 1 breast cancer is close to 100 percent; for stage 2, it’s about 93 percent. Women with stage 3 and even stage 4 cancers also have many treatment options, but early detection offers the best chance of remission.
Those survival rates might be increasing, too, because of new research.
“Right now, we have several clinical trials taking place at UNC that are
advancing the science around breast cancer risk and progression,” Dr. Troester says. “We have a large team working together to identify and study the different types of breast cancers. This is exciting because it will help doctors figure out the best prevention strategies and best treatments to obtain the optimal outcomes for each specific type of breast cancer.”
f you’re concerned about your cancer risk, talk to your doctor. If you do not have a doctor, find one near you.