There are no rules about who gets this disease. The two most significant risk factors are being a woman, and increasing age. However, there are other factors that may increase your risk, and some that may lower it.
The development of breast cancer may be influenced by factors that affect the levels of female hormones that circulate in your body throughout life. These factors include the age when you began your menstrual period, the number of times you have been pregnant, your age at first pregnancy, whether you have breastfed your children, and your level of physical activity.
Explaining the concept of cancer risk is one of the ongoing challenges of public health education. Medical research has defined risk factors for developing breast and ovarian cancer by studying large populations of women. It is important to remember that most risk factors increase the chance of getting cancer by only a small amount above the general or "baseline" risk.
For example, if something increases the risk of developing cancer by a factor of 2 — meaning that the risk is doubled — that sounds frightening. However, if the baseline risk of getting the cancer is 1 in 100,000, doubling the risk means that the figure is still only 2 in 100,000.
Given this information, an individual woman will not know whether having a particular risk factor means she will get cancer. Rather, it is one of many factors that can guide her in making health and lifestyle choices.
All in the Family
Women are often confused by what it means to have a family history of breast or ovarian cancer. Doctors usually look only at very close blood relatives — your mother, sisters and daughters — when determining your family history of these diseases. If one or more of these relatives has had breast or ovarian cancer, your own risk is significantly increased.
If a grandmother, aunt or cousin has been diagnosed with the disease, however, your personal risk is usually not significantly changed, unless many of these "secondary" relatives have had the disease.
Risk Factors for Breast Cancer
- Age — The older you are, the greater your chance of getting breast cancer. Experts believe that one in eight women who live to age 80 will get the disease. About 77 percent of women are over age 50 at the time they are diagnosed with breast cancer; less than 1 percent are diagnosed in their 20s. When younger women — those who have not gone through menopause — get the disease, it may be a faster-growing breast cancer.
- Family History — If you have a close blood relative — a mother, sister or daughter — who has had breast cancer, your own risk for developing the disease doubles. If two of these relatives have the disease, your risk increases five times.
In many cases where breast cancer seems to run in families, a mutation in specific genes, called BRCA1 and BRCA2, may be contributing to the cancer. Genetic tests are available to see if a woman carries this mutation. However, genetic testing is a complex area. If you have concerns about your family history, you should consult a doctor and a genetic counselor who can help you weigh the benefits and risks of testing.
- Personal History — A woman with cancer in one breast has a three to four-fold increased risk of developing a new cancer in the other breast.
- Race — White women are slightly more likely to develop breast cancer than are African-American women. African-Americans are more likely to die of this cancer, however. Asian and Hispanic women have a lower risk of developing breast cancer.
- Other Breast Disease — Although most benign breast disease does not increase your risk of developing breast cancer, a biopsy result that shows a condition called atypical hyperplasia, or proliferative breast disease without atypia, does increase the risk to some extent.
- Previous Breast Irradiation — If you received radiation therapy to your chest when you were a child or young woman — for example, for treatment of Hodgkin's disease or non-Hodgkin's lymphoma — your risk of developing breast cancer is slightly increased.
- Menstrual Periods — If you started menstruating before age 12 or if you went through menopause after age 50, your risk for breast cancer is slightly increased.
- Oral Contraceptives — Women who use oral contraceptives (birth control pills) may under certain circumstances have a slightly greater risk of getting breast cancer, but the link is not clear.
- Not Having Children — If you have not had children, or had your first child after age 30, your risk for breast cancer is slightly increased. Having an abortion or miscarriage does not seem to affect the overall risk.
- Not Breastfeeding — Your breast cancer risk may be slightly lowered if you breastfeed your children, especially if you continue nursing for 1.5 to 2 years.
- Hormone Replacement Therapy (HRT) — Some women choose to take hormones containing estrogen, with or without a form of progesterone, after menopause. Long-term use — 10 years or more — of HRT may slightly increase the risk of breast cancer. The risk seems to return to normal within five years of stopping HRT. This risk must be weighed against the many health benefits of using HRT.
- Alcohol — This is clearly linked to an increased risk for breast cancer. Those who have two to five alcoholic drinks daily have 1.5 times the risk for developing breast cancer as women who do not drink. Reducing your alcoholic intake to no more than three servings per week is recommended.
- Weight and Diet — Women who are overweight, especially after menopause, are at increased risk for breast cancer. Researchers believe that this is because fat tissue can make estrogen, and exposure to estrogen is linked to breast cancer. Researchers have not yet found a clear link between high-fat diets and breast cancer, although such a relationship has been shown for other cancers.
- Physical Activity — Recent studies indicate that even moderate exercise may help to lower your breast cancer risk. This link is being investigated further.
- Exposure to Environmental Pollutants — Research has not shown a clear link between breast cancer risk and exposure to pollutants such as pesticides (DDE and DDT) and polychlorinated biphenyls (PCBs). However, the subject of environmental pollutants and cancer is complex and requires further study.
Reviewed by health care specialists at UCSF Medical Center.
This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.