A risk factor is anything that increases your chance of getting a disease, such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx, bladder, kidney, and several other organs.
But having a risk factor, or even several, does not mean that you will get the disease. Some women who have one or more breast cancer risk factors never develop the disease, while most women with breast cancer have no apparent risk factors. Even when a woman with breast cancer has a risk factor, there is no way to prove that it actually caused her cancer.
There are different kinds of risk factors. Some factors, like a person's age or race, can't be changed. Others are linked to cancer-causing factors in the environment. Still others are related to personal choices such as smoking, drinking, and diet. Some factors influence risk more than others, and your risk for breast cancer can change over time. Getting older, a new breast biopsy result, or a new diagnosis of breast cancer in your family could change your risk.
Risk Factors That Cannot be Changed
Gender: Simply being a woman is the main risk factor for developing breast cancer. Because women have many more breast cells than men do and perhaps because their breast cells are constantly exposed to the growth-promoting effects of female hormones, breast cancer is much more common in women. Men can develop breast cancer, but this disease is about 100 times more common among women than men.
Aging: Your risk of developing breast cancer increases as you get older. About 18% of breast cancer diagnoses are among women in their 40's, while about 77% of women with breast cancer are older than 50 when they are diagnosed.
Genetic risk factors: Recent studies have shown that about 10% of breast cancer cases are hereditary as a result of gene changes (mutations). The most common gene changes are those of the BRCA1 and BRCA2 genes. Normally, these genes help to prevent cancer by making proteins that keep cells from growing abnormally. However, if you have inherited a changed gene from either parent, your chances of developing breast cancer increase.
See the section Do We Know What Causes Breast Cancer? for more information about genes and DNA. Women with an inherited BRCA1 or BRCA2 mutation have a 50% to 85% chance of developing breast cancer during their lifetime. Women with these inherited mutations also have an increased risk for developing ovarian cancer.
Other genes have been discovered that might also lead to inherited breast cancers. One of these is the ATM gene. ATM stands for ataxia-telangiectasia mutation. The gene is responsible for repairing damaged DNA. Certain families with a high rate of breast cancer have been found to have mutations of this gene. Another gene, the CHEK-2 gene, also increases breast cancer risk when it is mutated. Very recently, scientists have also found increased breast cancer risk associated with changes in genes linked to the BRCA genes. This may affect their ability to function.
Inherited mutations of the p53 tumor suppressor gene can also increase your risk of developing breast cancer, as well as leukemia, brain tumors, and/or sarcomas (cancer of bones or connective tissue). The Li-Fraumeni syndrome, named after the 2 researchers who described this inherited cancer syndrome, is a rare cause of breast cancer.
If you are considering genetic testing, we strongly recommend that first you talk to a genetic counselor, nurse, or doctor qualified to interpret and explain these test, before being tested. It is very important to understand and carefully weigh the benefits and risks of genetic testing before these tests are done. Testing is expensive and is not covered by some health plans. There is concern that people with abnormal genetic test results will not be able to get life insurance or that coverage may only be available at a much higher cost. For more information, see our position statement on genetic testing.
Family history of breast cancer: Breast cancer risk is higher among women whose close blood relatives have this disease. Blood relatives can be from either the mother's or father's side of the family. Having 1 first-degree relative (mother, sister, or daughter) with breast cancer approximately doubles your risk, and having 2 first-degree relatives increases your risk 5-fold. Although the exact risk is not known, women with a family history of breast cancer in a father or brother also have an increased risk of breast cancer.
Personal history of breast cancer: A woman with cancer in one breast has a 3- to 4-fold increased risk of developing a new cancer in the other breast or in another part of the same breast. This is different from a recurrence (return) of the first cancer.
Race: White women are slightly more likely to develop breast cancer than are African-American women. But African-American women are more likely to die of this cancer because their cancers are often diagnosed later and at an advanced stage when they are harder to treat and cure. There is also some question about whether African-American women have more aggressive tumors. Asian, Hispanic, and Native American women have a lower risk of developing breast cancer.
Previous breast biopsy: Women whose earlier breast biopsies detected proliferative breast disease without atypia or usual hyperplasia have a slightly higher risk of breast cancer (1.5 to 2 times greater than other women). Having a previous biopsy result of atypical hyperplasia increases a woman's breast cancer risk by 4 to 5 times. Having a biopsy specimen diagnosed as fibrocystic changes without proliferative breast disease does not affect breast cancer risk.
Previous breast irradiation: Women who as children or young adults have had radiation therapy to the chest area as treatment for another cancer (such as Hodgkin's disease or non-Hodgkin's lymphoma) have a significantly increased risk for breast cancer.
Menstrual periods: Women who started menstruating at an early age (before age 12) or who went through menopause at a late age (after age 50) have a slightly higher risk of breast cancer.