Breast Cancer Prevention

Key Points

• Avoiding risk factors and increasing protective factors may help prevent cancer.
• The following are risk factors for breast cancer:
  • Older age
  • A personal history of breast cancer or benign (noncancer) breast disease
  • Inherited risk of breast cancer
  • Dense breasts
  • Exposure of breast tissue to estrogen made in the body
  • Taking hormone therapy for symptoms of menopause
  • Radiation therapy to the breast or chest
  • Obesity
  • Drinking alcohol
• The following are protective factors for breast cancer:
  • Less exposure of breast tissue to estrogen made by the body
  • Taking estrogen-only hormone therapy after hysterectomy, selective estrogen receptor modulators, or aromatase inhibitors and inactivators
    • Estrogen-only hormone therapy after hysterectomy
    • Selective estrogen receptor modulators
    • Aromatase inhibitors and inactivators
  • Risk-reducing mastectomy
  • Ovarian ablation
  • Getting enough exercise
• It is not clear whether the following affect the risk of breast cancer:
  • Hormonal contraceptives
  • Environment
• Studies have shown that some factors have little or no effect on the risk of breast cancer.
• Cancer prevention clinical trials are used to study ways to prevent cancer.
• New ways to prevent breast cancer are being studied in clinical trials.

Avoiding risk factors and increasing protective factors may help prevent cancer.

Avoiding cancer risk factors may help prevent certain cancers. Risk factors include smoking, being overweight, and not getting enough exercise. Increasing protective factors such as quitting smoking and exercising may also help prevent some cancers. Talk to your doctor or other health care professional about how you might lower your risk of cancer.

NCI's Breast Cancer Risk Assessment Tool uses a woman's risk factors to estimate her risk for breast cancer during the next five years and up to age 90. This online tool is meant to be used by a health care provider.

The following are risk factors for breast cancer:

Older age

Older age is the main risk factor for most cancers. The chance of getting cancer increases as you get older.

A personal history of breast cancer or benign (noncancer) breast disease

Women with any of the following have an increased risk of breast cancer:

• A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
• A personal history of benign (noncancer) breast disease.

Inherited risk of breast cancer

Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.

Women who have inherited changes in the BRCA1 and BRCA2 genes or in certain other genes have a higher risk of breast cancer. The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.

Dense breasts

Having breast tissue that is dense on a mammogram is a factor in breast cancer risk. The level of risk depends on how dense the breast tissue is. Women with very dense breasts have a higher risk of breast cancer than women with low breast density.

Increased breast density is often an inherited trait, but it may also occur in women who have not had children, have a first pregnancy late in life, take postmenopausal hormones, or drink alcohol.

Exposure of breast tissue to estrogen made in the body

Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.

A woman's exposure to estrogen is increased in the following ways:

• Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
• Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
• Older age at first birth or never having given birth: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.

Taking hormone therapy for symptoms of menopause

Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.

Radiation therapy to the breast or chest

Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given. The risk is highest if radiation treatment was used during puberty, when breasts are forming.

Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.

For women who have inherited changes in the BRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.

Obesity

Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.

Drinking alcohol

Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.

The following are protective factors for breast cancer:

Less exposure of breast tissue to estrogen made by the body

Decreasing the length of time a woman's breast tissue is exposed to estrogen may help prevent breast cancer. Exposure to estrogen is reduced in the following ways:

• Early pregnancy: Estrogen levels are lower during pregnancy. Women who have a full-term pregnancy before age 20 have a lower risk of breast cancer than women who have not had children or who give birth to their first child after age 35.
• Breast-feeding: Estrogen levels may remain lower while a woman is breast-feeding. Women who breastfed have a lower risk of breast cancer than women who have had children but did not breastfeed.

Taking estrogen-only hormone therapy after hysterectomy, selective estrogen receptor modulators, or aromatase inhibitors and inactivators

Estrogen-only hormone therapy after hysterectomy

Hormone therapy with estrogen only may be given to women who have had a hysterectomy. In these women, estrogen-only therapy after menopause may decrease the risk of breast cancer. There is an increased risk of stroke and heart and blood vessel disease in postmenopausal women who take estrogen after a hysterectomy.

Selective estrogen receptor modulators

Tamoxifen and raloxifene belong to the family of drugs called selective estrogen receptor modulators (SERMs). SERMs act like estrogen on some tissues in the body, but block the effect of estrogen on other tissues.

Treatment with tamoxifen lowers the risk of estrogen receptor-positive (ER-positive) breast cancer and ductal carcinoma in situ in premenopausal and postmenopausal women at high risk. Treatment with raloxifene also lowers the risk of breast cancer in postmenopausal women. With either drug, the reduced risk lasts for several years or longer after treatment is stopped. Lower rates of broken bones have been noted in patients taking raloxifene.

Taking tamoxifen increases the risk of hot flashes, endometrial cancer, stroke, cataracts, and blood clots (especially in the lungs and legs). The risk of having these problems increases markedly in women older than 50 years compared with younger women. Women younger than 50 years who have a high risk of breast cancer may benefit the most from taking tamoxifen. The risk of having these problems decreases after tamoxifen is stopped. Talk with your doctor about the risks and benefits of taking this drug. 

Taking raloxifene increases the risk of blood clots in the lungs and legs, but does not appear to increase the risk of endometrial cancer. In postmenopausal women with osteoporosis (decreased bone density), raloxifene lowers the risk of breast cancer for women who have a high or low risk of breast cancer. It is not known if raloxifene would have the same effect in women who do not have osteoporosis. Talk with your doctor about the risks and benefits of taking this drug.

Other SERMs are being studied in clinical trials.

Aromatase inhibitors and inactivators

Aromatase inhibitors (anastrozole, letrozole) and inactivators (exemestane) lower the risk of recurrence and of new breast cancers in women who have a history of breast cancer. Aromatase inhibitors also decrease the risk of breast cancer in women with the following conditions:

• Postmenopausal women with a personal history of breast cancer.
• Women with no personal history of breast cancer who are 60 years and older, have a history of ductal carcinoma in situ with mastectomy, or have a high risk of breast cancer based on the Gail model tool (a tool used to estimate the risk of breast cancer).

In women with an increased risk of breast cancer, taking aromatase inhibitors decreases the amount of estrogen made by the body. Before menopause, estrogen is made by the ovaries and other tissues in a woman's body, including the brain, fat tissue, and skin. After menopause, the ovaries stop making estrogen, but the other tissues do not. Aromatase inhibitors block the action of an enzyme called aromatase, which is used to make all of the body's estrogen. Aromatase inactivators stop the enzyme from working.

Possible harms from taking aromatase inhibitors include muscle and joint pain, osteoporosis, hot flashes, and feeling very tired.

Risk-reducing mastectomy

Some women who have a high risk of breast cancer may choose to have a risk-reducing mastectomy (the removal of both breasts when there are no signs of cancer). The risk of breast cancer is much lower in these women and most feel less anxious about their risk of breast cancer. However, it is very important to have a cancer risk assessment and counseling about the different ways to prevent breast cancer before making this decision.

Ovarian ablation

The ovaries make most of the estrogen that is made by the body. Treatments that stop or lower the amount of estrogen made by the ovaries include surgery to remove the ovaries, radiation therapy, or taking certain drugs. This is called ovarian ablation.

Premenopausal women who have a high risk of breast cancer due to certain changes in the BRCA1 and BRCA2 genes may choose to have a risk-reducing oophorectomy (the removal of both ovaries when there are no signs of cancer). This decreases the amount of estrogen made by the body and lowers the risk of breast cancer. Risk-reducing oophorectomy also lowers the risk of breast cancer in normal premenopausal women and in women with an increased risk of breast cancer due to radiation to the chest. However, it is very important to have a cancer risk assessment and counseling before making this decision. The sudden drop in estrogen levels may cause the symptoms of menopause to begin. These include hot flashes, trouble sleeping, anxiety, and depression. Long-term effects include decreased sex drive, vaginal dryness, and decreased bone density.

Getting enough exercise

Women who exercise four or more hours a week have a lower risk of breast cancer. The effect of exercise on breast cancer risk may be greatest in premenopausal women who have normal or low body weight.

It is not clear whether the following affect the risk of breast cancer:

Hormonal contraceptives

Hormonal contraceptives contain estrogen or estrogen and progestin. Some studies have shown that women who are current or recent users of hormonal contraceptives may have a slight increase in breast cancer risk. Other studies have not shown an increased risk of breast cancer in women using hormonal contraceptives.

In one study, the risk of breast cancer slightly increased the longer a woman used hormonal contraceptives. Another study showed that the slight increase in breast cancer risk decreased over time when women stopped using hormonal contraceptives.

More studies are needed to know whether hormonal contraceptives affect a woman's risk of breast cancer.

Environment

Studies have not proven that being exposed to certain substances in the environment, such as chemicals, increases the risk of breast cancer.

Studies have shown that some factors have little or no effect on the risk of breast cancer.

The following have little or no effect on the risk of breast cancer:

• Having an abortion.
• Making diet changes such as eating less fat or more fruits and vegetables.
• Taking vitamins, including fenretinide (a type of vitamin A).
• Cigarette smoking, both active and passive (inhaling secondhand smoke).
• Using underarm deodorant or antiperspirant.
• Taking statins (cholesterol -lowering drugs).
• Taking bisphosphonates (drugs used to treat osteoporosis and hypercalcemia) by mouth or by intravenous infusion.
• Working night shifts, which may change your circadian rhythm (physical, mental, and behavioral changes that are mainly affected by darkness and light in 24 hour cycles).

Cancer prevention clinical trials are used to study ways to prevent cancer.

Cancer prevention clinical trials are used to study ways to lower the risk of developing certain types of cancer. Some cancer prevention trials are conducted with healthy people who have not had cancer but who have an increased risk for cancer. Other prevention trials are conducted with people who have had cancer and are trying to prevent another cancer of the same type or to lower their chance of developing a new type of cancer. Other trials are done with healthy volunteers who are not known to have any risk factors for cancer.

The purpose of some cancer prevention clinical trials is to find out whether actions people take can prevent cancer. These may include exercising more or quitting smoking or taking certain medicines, vitamins, minerals, or food supplements.