What are the risk factors for breast cancer?
Certain changes in DNA can cause normal breast cells to become cancer. DNA is the substance 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. These changes 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, 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.
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 from 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 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, so not having a relative with breast cancer doesn’t mean you won’t get it.
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 a recurrence).
Race: Overall, white women are slightly more likely to get breast cancer than African-American women. African American women, though, are more likely to die of breast cancer. And in women under 45 years of age, breast cancer is more common in African American women. 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: In this condition, cells that look like cancer cells are in the milk-making glands (lobules), but they do not grow 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 in either breast 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 she 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.
Treatment with DES: In the past, some pregnant women were given the drug DES (diethylstilbestrol) because it was thought to lower their chances of losing the baby (miscarriage). Studies have shown that these women have a slightly increased risk of getting breast cancer. The effect on the children exposed in the womb is less clear, but they may also have a slightly higher risk of breast cancer. For more information on DES see our document, DES Exposure: Questions and Answers.
Breast cancer risk and lifestyle choices
Not having children or having them later in life: Women who have had not had children, or who had their first child after age 30, have a slightly higher risk of breast cancer. Being pregnant many times and at an early age reduces breast cancer risk. Being pregnant lowers a woman’s total number of lifetime menstrual cycles, which may be the reason for this effect.
Recent use of birth control pills: Studies have found that women who are using birth control pills have a slightly greater risk of breast cancer than women who have never used them. This risk seems to go back to normal over time once the pills are stopped. Women who stopped using the pill more than 10 years ago do not seem to have any increased risk. It's a good idea to talk to your doctor about the risks and benefits of birth control pills.
Depot-medroxyprogesterone acetate (DMPA or Depo-Provera®) is an injectable form of progesterone that is given once every 3 months as a “shot” for birth control. Women now using DMPA seem to have an increase in breast cancer risk, but the risk doesn’t seem to be increased if this drug was stopped more than 5 years ago.
Using hormone therapy after menopause: Post-menopausal hormone therapy (PHT) has been used for many years to help relieve symptoms of menopause and to help prevent thinning of the bones (osteoporosis). This treatment goes by other names, such as hormone replacement therapy (HRT), and menopausal hormone therapy (MHT).
There are 2 main types of PHT. For women who still have a womb (uterus), doctors most often prescribe both estrogen and progesterone (known as combined hormone therapy or combined HT). Estrogen alone can increase the risk of cancer of the uterus, so progesterone is needed to help prevent this. For women who no longer have a uterus (those who’ve had a hysterectomy), estrogen alone can be prescribed. This is known as estrogen replacement therapy (ERT) or just estrogen therapy (ET).
- Combined HT: Use of combined HT after menopause increases the risk of getting breast cancer. It may also increase the chances of dying from breast cancer. Breast cancer in women taking hormones may also be found at a more advanced stage, perhaps because it lowers how well mammograms work by increasing breast density. Five years after stopping HT, the breast cancer risk seems to drop back to normal. The word bioidentical is sometimes used to describe versions of estrogen and progesterone with the same chemical structure as those found naturally in people. The use of these hormones has been marketed as a safe way to treat the symptoms of menopause. It is important to keep in mind that although there are few studies comparing “bioidentical" or “natural” hormones to man-made versions of hormones, there is no evidence that they are safer or work better. The use of these bioidentical hormones should be assumed to have the same health risks as any other type of hormone therapy.
- ET: The use of estrogen alone does not seem to increase the risk of developing breast cancer. In fact, some research has seemed to show that women who have had their uterus removed and who take estrogen actually have a lower risk of breast cancer. But women taking estrogen seem to have more problems with strokes and other blood clots. And when used for a long time (for more than 10 years), some studies have found that ET increases the risk of ovarian cancer.
At this time, there seem to be few strong reasons to use PHT, other than for short-term relief of menopausal symptoms. Because there are other factors to think about, you should talk with your doctor about the pros and cons of using PHT. If you and your doctor decide to try PHT for symptoms of menopause, it is usually best to use it at the lowest dose that works for you and for as short a time as possible.
Not breastfeeding: Some studies have shown that breastfeeding slightly lowers breast cancer risk, especially if the breastfeeding lasts 1½ to 2 years. This could be because breastfeeding lowers a woman’s total number of menstrual periods, as does pregnancy. But this has been hard to study because, in countries such as the United States, breastfeeding for this long is uncommon.
Alcohol: The use of alcohol is clearly linked to an increased risk of getting breast cancer. Women who have one drink a day have a very small increased risk. Those who have 2 to 5 drinks daily have about 1½ times the risk of women who don’t drink alcohol. Too much alcohol use is also known to increase the risk of several other types of cancer.
Being overweight or obese: Being overweight or obese after menopause (or because of weight gain that took place as an adult) is linked to a higher risk of breast cancer. But the link between weight and breast cancer risk is complex. The risk seems to be higher if the extra fat is around the waist.
Lack of exercise: Studies show that exercise reduces breast cancer risk. The only question is how much exercise is needed. One study found that as little as 1 hour and 15 minutes to 2½ hours of brisk walking per week reduced the risk by 18%. Walking 10 hours a week reduced the risk a little more.
Risk factors that are not certain or that haven’t been proven
Diet and vitamin intake: Many studies have looked for a link between what women eat and breast cancer risk, but so far there are no clear answers. Some studies seemed to show that diet may play a role, while others found no evidence that diet has an effect on breast cancer risk. Studies have looked at the amount of fat in the diet, intake of fruits and vegetables, and intake of meat. No clear link to breast cancer risk was found. Studies have also looked at vitamin levels, but again the results are not clear. So far, no study has shown that taking vitamins lowers breast cancer risk. This is not to say that there is no point in eating a healthy diet. A diet low in fat, low in red meat and processed meat, and high in fruits and vegetables can have many health benefits.
Most studies found that breast cancer is less common in countries where the typical diet is low in fat. On the other hand, many studies of women in the United States have not found breast cancer risk to be linked to how much fat they ate. Researchers are still not sure how to explain this difference. More research is needed to better understand the effect of the types of fat eaten and body weight on breast cancer risk.
Antiperspirants and bras: Internet e-mail rumors have suggested that underarm antiperspirants can cause breast cancer. There is very little evidence to support this idea. A large study of breast cancer causes found no increase in breast cancer in women who used antiperspirants. Also, there is no evidence to support the idea that bras cause breast cancer.
Induced abortions: Several studies show that induced abortions do not increase the risk of breast cancer. Also, there is no evidence to show a direct link between miscarriages and breast cancer. For more detailed information, see our document, Is Abortion Linked to Breast Cancer?
Breast implants: Silicone breast implants can cause scar tissue to form in the breast. But studies have found that this does not increase breast cancer risk. If you have breast implants, you might need special x-ray pictures during mammograms.
Pollution: A lot of research is being done to learn how the environment might affect breast cancer risk. This issue understandably invokes a great deal of public concern, but at this time research does not show a clear link between breast cancer risk and exposure to things like plastics, certain cosmetics and personal care products, and pesticides (such as DDE). More research is needed to better define the possible health effects of these and similar compounds.
Tobacco smoke: For a long time, studies found no link between active cigarette smoking and breast cancer. In recent years, though, more studies have found that smoking may increase the risk of breast cancer. The increased risk seems to affect certain groups, such as women who started smoking when they were young. In 2009, the International Agency for Research on Cancer concluded that there is limited evidence that tobacco smoking causes breast cancer.
An issue that continues to be a focus of research is whether secondhand smoke (smoke from another person's cigarette) may increase the risk of breast cancer. But the evidence about secondhand smoke and breast cancer risk in human studies is not clear. In any case, a possible link to breast cancer is yet another reason to avoid being around secondhand smoke.
Night work: A few studies have suggested that women who work at night (nurses on the night shift, for instance) have a higher risk of breast cancer. This is a fairly recent finding, and more studies are being done to look at this.
Last Medical Review: 09/04/2012
Last Revised: 02/22/2013