What are the risk factors for breast cancer?

Certain changes in DNA can cause normal breast cells to become cancer. DNA is the chemical in each of our cells that makes up our genes — the instructions for how our cells work. Some inherited DNA changes (mutations) can increase the risk for developing cancer and cause the cancers that run in some families. For instance, BRCA1 and BRCA2 are tumor suppressor genes — they keep cancer tumors from forming. When they are changed (mutated), they no longer cause cells to die at the right time, and cancer is more likely to develop.

But most breast cancer DNA changes happen in single breast cells during a woman's life rather than having been inherited. So far, the causes of most of the DNA mutations that could lead to breast cancer are not known.

Risk factors

While we do not yet know exactly what causes breast cancer, we do know that certain risk factors are linked to the disease. A risk factor is something that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, such as smoking, drinking, and diet are linked to things a person does. Others, like a person's age, race, or family history, can't be changed.

But risk factors don't tell us everything. Having a risk factor, or even several, doesn't mean that a woman will get breast cancer. Some women who have one or more risk factors never get the disease. And most women who do get breast cancer don't have any risk factors (other than being a woman and growing older). Some risk factors have a greater impact than others, and your risk for breast cancer can change over time, due to factors such as aging or lifestyle.
Although many risk factors may increase your chance of having breast cancer, it is not yet known just how some of these risk factors cause cells to become cancer. Hormones seem to play a role in many cases of breast cancer, but just how this happens is not fully understood.

Risk factors you cannot change

Gender: Being a woman is the main risk for breast cancer. While men also get the disease, it is about 100 times more common in women than in men.

Age: The chance of getting breast cancer goes up as a woman gets older. About 2 of 3 women with invasive breast cancer are 55 or older when the cancer is found.

Genetic risk factors: About 5% to 10% of breast cancers are thought to be linked to inherited changes (mutations) in certain genes. The most common gene changes are those of the BRCA1 and BRCA2 genes. Women with these gene changes have up to an 80% chance of getting breast cancer during their lifetimes. Other gene changes may raise breast cancer risk, too.

Family history: Breast cancer risk is higher among women whose close blood relatives have this disease. The relatives can be from either the mother's or father's side of the family. Having a mother, sister, or daughter with breast cancer about doubles a woman's risk. It's important to note that most (over 85%) women who get breast cancer do not have a family history of this disease.

Personal history of breast cancer: A woman with cancer in one breast has a greater chance of getting a new cancer in the other breast or in another part of the same breast. This is different from a return of the first cancer (called recurrence).

Race: Overall, white women are slightly more likely to get breast cancer than African-American women. But in women under 45 years of age, breast cancer is more common in African American women. African American women, though, are more likely to die of breast cancer. Asian, Hispanic, and Native-American women have a lower risk of getting and dying from breast cancer.

Dense breast tissue: Dense breast tissue means there is more gland tissue and less fatty tissue. Women with denser breast tissue have a higher risk of breast cancer. Dense breast tissue can also make it harder for doctors to spot problems on mammograms.

Certain benign (not cancer) breast problems: Women who have certain benign breast changes may have an increased risk of breast cancer. Some of these are more closely linked to breast cancer risk than others. For more details about these, see our document, Non-cancerous Breast Conditions.

Lobular carcinoma in situ: This begins in the milk-making glands (lobules) but does not go through the wall of the lobules and cannot spread to other parts of the body. It is not a true cancer or pre-cancer, but having LCIS increases a woman's risk of getting cancer later. For this reason, it's important that women with LCIS make sure they have regular mammograms and doctor visits. Women with lobular carcinoma in situ (LCIS) have a 7 to 11 times greater risk of developing cancer in either breast.

Menstrual periods: Women who began having periods early (before age 12) or who went through the change of life (menopause) after the age of 55 have a slightly increased risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the hormones estrogen and progesterone.

Breast radiation early in life: Women who have had radiation treatment to the chest area (as treatment for another cancer) earlier in life have a greatly increased risk of breast cancer. The risk varies with the patient's age when they had radiation. The risk from chest radiation is highest if the radiation were given during the teens, when the breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk.