At the most basic level, breast cancer risk is influenced by our gender and our age: breast cancer is much more common in women than in men, and our risk increases as we age. Beyond these two factors, however, are a number of risk factors that we may be able to change or that may influence how we manage our breast cancer risk. It’s also worth noting which factors either don’t affect breast cancer risk or have an uncertain relationship based on available evidence. The goal? Focusing our energy on the things that matter most.
Although some risk factors are out of our control, being aware of them can help us manage our risk.
The bad news is that many of the factors that have the biggest effect on breast cancer risk—such as inherited gene mutations—are things we cannot control. The good news is that information about these risk factors can help us take steps to reduce our risk.
BRCA1/2 mutation. Of all the risk factors discussed in this article, inherited mutations in the BRCA1 or BRCA2 genes have the greatest impact on breast cancer risk. Mutations in these genes (which also increase the risk of ovarian cancer) can be passed down through either the mother’s or the father’s side of the family and occur more frequently in people of Ashkenazi Jewish descent. If genetic testing reveals that you carry one of these gene mutations, options to manage your cancer risk include early and more-intensive screening, medications to reduce cancer risk, and preventive surgery to remove the breasts and/or ovaries before cancer develops.1
Family history. Even if your family doesn’t have a BRCA1/2 mutation, a family history of breast cancer increases your risk. Breast cancer in a close relative (your mother or sister, for example) increases your risk to a greater extent than breast cancer in a more distant relative, particularly if the cancer is diagnosed at a young age.
Breast density. Breast density can be evaluated by mammography and refers to the extent of glandular and connective tissue in the breasts. Breasts with more glandular and connective tissue—and less fat—are denser. Women with higher breast density are at increased risk of developing breast cancer.2
Benign breast disease. Benign breast disease refers to several types of non-cancerous changes in breast tissue. Although some of these breast changes have very little (or no) effect on subsequent breast cancer risk, others—particularly atypical hyperplasia—are linked with increased risk.3 In atypical hyperplasia the number of cells within the ducts or lobules of the breast is increased, and these cells appear abnormal under a microscope.
Radiation to the chest. Women who received radiation therapy to the chest at a young age for the treatment of Hodgkin’s lymphoma or other cancers have an increased risk of breast cancer.4
Reproductive factors. Early age at first menstrual period, late age at first birth, and late age at menopause all increase the risk of breast cancer. The timing of a first birth is, arguably, within our control but is usually driven by considerations other than cancer risk.
Risk Factors That You Can Control
Several other factors have less of an effect on breast cancer risk than some of the factors mentioned above but are worth knowing about because they’re things that we can control.
Alcohol. Even moderate drinking can increase the risk of breast cancer: each 10 gram (slightly less than one drink) increase in daily alcohol consumption increases the risk of breast cancer by an estimated 7 to 10 percent.5,6 Although this is a fairly modest increase in risk, breast cancer is a common cancer; even a small increase in risk may translate into many additional cases on a population level.
Postmenopausal hormonetherapy. The effect of postmenopausal hormone therapy on breast cancer appears to vary by the type of hormone therapy: combined estrogen plus progestin is linked with an increased risk of breast cancer, whereas estrogen alone may actually decrease breast cancer risk.7 Because estrogen alone can cause endometrial (uterine) cancer, is it generally used only by women who have had a hysterectomy.
Body weight. In premenopausal women, obesity has been linked with a decreased risk of breast cancer, possibly as a result of disrupted menstrual cycles and altered hormone levels. In postmenopausal women, however, obesity is linked with an increased risk of breast cancer. After menopause (when ovarian hormone production drops dramatically), estrogen continues to be produced in fat tissue; higher estrogen levels in heavier women may explain the link with breast cancer.
Physical activity. In addition to decreasing your risk of developing breast cancer, regular physical activity may improve survival after a breast cancer diagnosis.8,9
Exposures That Probably Don’t Affect the Risk of Breast Cancer
At one time or another, the following exposures have been in the news (or circulated on the Internet) as possibly linked with breast cancer. The best available evidence, however, suggests that these factors do not affect the risk of breast cancer.
Abortion. Some early studies raised concerns about a link between abortion and breast cancer, but this link was not confirmed by later studies.10,11 In 2009 the American College of Obstetricians and Gynecologists issued a committee opinion that stated, “More rigorous recent studies demonstrate no causal relationship between induced abortion and a subsequent increase in breast cancer risk.”12
Underwire bras. Most experts agree that it’s simply not plausible that wearing a bra would affect your risk of breast cancer.13,14 Restriction of the breasts would not be expected to affect hormone levels or other factors linked with breast cancer development.
Antiperspirants. Internet rumors fueled concerns about a link between underarm antiperspirants/deodorants and breast cancer, but a National Cancer Institute fact sheet on the topic states, “Researchers at the National Cancer Institute (NCI), a part of the National Institutes of Health, are not aware of any conclusive evidence linking the use of underarm antiperspirants or deodorants and the subsequent development of breast cancer. The US Food and Drug Administration (FDA), which regulates food, cosmetics, medicines, and medical devices, also does not have any evidence or research data that ingredients in underarm antiperspirants or deodorants cause cancer.”15
Environmental pollutants. Although the health effects of environmental contaminants are a concern for all of us, it remains uncertain whether exposure to these agents affects breast cancer risk. This is an active area of research, however; scientists continue to explore the effects of many different types of chemicals and pollutants, including those termed “endocrine disrupters” (chemicals that affect the production or function of hormones such as estrogen).16
Focusing Our Efforts
By learning about which factors do (and do not) affect breast cancer risk, we can focus our energy on those behaviors that provide the greatest benefit. This is also an important point to keep in mind as we advocate for additional breast cancer research: it doesn’t help anyone to pursue topics that are catchy but unlikely to yield results.
2.Boyd N, Guo H, Martin L, et al. Mammographic density and the risk and detection of breast cancer. New England Journal of Medicine. 2007;356:227-36.
3.London SJ, Connolly JL, Schnitt SJ, Colditz GA. A prospective study of benign breast disease and the risk of breast cancer. Journal of the American Medical Association. 1992;267:941-44.
4.Travis LB, Hill DA, Dores GM, et al. Breast cancer following radiotherapy and chemotherapy among young women with Hodgkin disease. Journal of the American Medical Association. 2003;290:465-75.
5.Collaborative Group on Hormonal Factors in Breast Cancer. Alcohol, tobacco and breast cancer—collaborative reanalysis of individual data from 53 epidemiological studies, including 58,515 women with breast cancer and 95,067 without the disease. British Journal of Cancer. 2002;87:1234-45.
6.Key J, Hodgson S, Omar RZ, et al. Meta-analysis of alcohol and breast cancer with consideration of the methodological issues. Cancer Causes and Control. 2006;17:759-70.
7.LaCroix AZ, Chlebowski RT, Manson JE, et al. Health outcomes after stopping conjugated equine estrogens among postmenopausal women with prior hysterectomy: a randomized controlled trial. Journal of the American Medical Association. 2011;305:1305-14.
8.Scientific Program Committee. Physical activity across the cancer continuum: report of a workshop. Review of existing knowledge and innovative designs for future research. Cancer. 2002;95:1134-43.
9.Holmes MD, Chen WY, Feskanich D, Kroenke CH, Colditz GA. Physical activity and survival after breast cancer diagnosis. Journal of the American Medical Association. 2005;293:2479-86.
10.Reeves GK, Kan SW, Key T, et al. Breast cancer risk in relation to abortion: results from the EPIC study. International Journal of Cancer. 2006;119:1741-45.
11.Beral V, Bull D, Doll R, Peto R, Reeves G. Collaborative Group of Hormonal Factors in Breast Cancer. Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries. Lancet. 2004;363:1007-16.
12.Committee on Gynecologic Practice. ACOG Committee opinion no. 434: induced abortion and breast cancer risk. Obstetrics and Gynecology. 2009;113(6):1417-18.
Tools to Help You Estimate Your Risk
Breast Cancer Risk Assessment Tool (National Cancer Institute):
Your Disease Risk (Siteman Cancer Center): www.yourdiseaserisk.wustl.edu