Breast Cancer Prevention

by Specialist

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

Avoiding risk factors for cancer can help prevent some cancers. These risk factors include smoking, being overweight, and not getting enough exercise.Adding protective factors such as quitting smoking and exercising may help prevent certain cancers.Consult your physician or other health care professional about how to reduce your cancer risk.

The NCI’s Breast Cancer Risk Assessment Tool uses an individual woman’s known risk factors to assess her risk of developing breast cancer over the next 5 years to age 90.This online tool is primarily for use by health care providers.For more information on breast cancer risk, call 1-800-4-CANCER.

The following are risk factors for breast cancer:

Advanced age

Advanced age is a major risk factor for most cancers.The risk of developing cancer rises as you get older.

History of breast cancer or benign (non-neoplastic) breast disease

Women who have any of the following are at increased risk of breast cancer:

  • Individuals who have had invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
  • Individuals who have had benign (non-neoplastic) breast disease.

    Genetic risk of breast cancer

    Women with a first-degree relative (mother, sister, or daughter) who has breast cancer are at increased risk of developing breast cancer themselves.

    Women with a related gene or genetic alteration in some specific gene have a higher risk of developing breast cancer.The risk of breast cancer caused by genetic alterations depends on the type of gene mutation, family history of cancer, and other factors.

    Dense breast

    Dense breast tissue, as suggested by a mammogram, is a risk factor for breast cancer.The degree of risk depends on how dense the breast tissue is.Women with high breast densities have a higher risk of breast cancer than women with low breast densities.

    High breast densities are usually a genetic trait, but may also occur in women who have never had children, have an older first pregnancy, use hormones after menopause, or drink alcohol.

    Exposure of breast tissue to estrogen in the body

    Estrogen is a hormone produced by the body.It can promote the body’s development and maintain female sexual characteristics.Prolonged exposure to estrogen may increase the risk of breast cancer.Estrogen levels are highest in women after the onset of menstruation.

    The following ways increase a woman’s estrogen exposure:

  • Early age of menarche: Menstruation at or before age 11 increases the number of years that breast tissue is exposed to estrogen.
  • Delayed menopause: The more years a woman is in her menstrual cycle, the longer her mammary glands are exposed to estrogen.
  • Advanced age at first birth or never had children: Breast tissue is exposed to more estrogen in women who have their first pregnancy after age 35 or never had children because of low estrogen levels during pregnancy.

    Treatment with hormones during menopause

    Hormones such as estrogen and progesterone can be synthesized.For postmenopausal or oophorectomized women who no longer produce estrogen, estrogen and progestin medications can be used alone or in combination for replacement therapy.This approach is known as hormone replacement therapy (HRT) or hormone therapy (HT).Combined HRT/HT is a combination of estrogen and progestin therapy.This type of HRT/HT can increase the risk of breast cancer.Some studies have shown a decrease in breast cancer risk after women stop using combined estrogen and progestin drugs.

    Radiotherapy to the breast or chest

    Women who receive radiotherapy to the chest because of cancer treatment have an increased risk of breast cancer, and this risk begins in the 10th year after treatment.The increased risk of breast cancer depends on the dose of radiation therapy and the age at which the radiation therapy is received.The risk of breast cancer is highest if you receive radiotherapy when the breast begins to develop during puberty.

    Treatment of one side of the breast with radiation therapy does not increase the risk of cancer in the opposite breast.

    Women with mutations in the BRCA1 and BRCA2 genes exposed to radiation similar to chest x-rays may have an increased risk of future breast cancer, especially if they have received an x-ray before age 20.

    Obesity

    Obesity increases the risk of breast cancer, especially in women who are not on hormone replacement therapy after menopause.

    Alcohol consumption

    Alcohol consumption increases the risk of breast cancer.As alcohol consumption increases, the risk increases.

    The following are protective factors for breast cancer:

    Reducing breast tissue exposure to estrogen in the body

    Reducing the amount of time a woman’s breast tissue is exposed to estrogen can help prevent breast cancer.Estrogen exposure can be reduced in the following ways:

  • Early age of 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 have their first pregnancy after age 35.
  • Breastfeeding: Estrogen levels may remain low while a woman is breastfeeding.Breastfeeding women have a lower risk of breast cancer than women who have given birth but have not breastfed.

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

    Estrogen-only therapy after hysterectomy

    Estrogen-only therapy can be used in women who have undergone hysterectomy.In premenopausal women, estrogen-only therapy may reduce the risk of breast cancer.In postmenopausal women, posthysterectomy estrogen therapy may increase the risk of stroke and cardiovascular disease.

    Selective estrogen receptor modulators

    Tamoxifen and raloxifene belong to the selective estrogen receptor modulator (SERM) class of drugs.SERM drugs act like estrogen in some tissues in the body, but block the effects of estrogen on other tissues.

    For premenopausal and postmenopausal women at high risk, tamoxifen treatment reduces the risk of estrogen receptor-positive (ER-positive) breast cancer and ductal carcinoma in situ.Raloxifene treatment may also reduce the risk of breast cancer in postmenopausal women.Regardless of which drug is used, the risk reduction can last for several years or longer after treatment ends.It is important to note that patients using raloxifene have a lower rate of fractures.

    Treatment with tamoxifen increases the risk of hot flashes, endometrial cancer, stroke, cataracts, and blood clots (especially in the lungs and legs).Women over 50 years of age have a significantly increased risk of these diseases compared to younger women.Women under 50 years of age at high risk for breast cancer may benefit most from treatment with tamoxifen.The risk of these diseases decreases when tamoxifen is discontinued.Consult your doctor about the risks and benefits of using this drug.

    Treatment with raloxifene increases the risk of blood clots in the lungs and legs, but does not increase the risk of endometrial cancer.In postmenopausal women with comorbid osteoporosis (reduced bone density), raloxifene may reduce the risk of breast cancer in both high-risk and low-risk women.It is not clear whether raloxifene will have the same effect in women without osteoporosis.Consult your doctor about the risks and benefits of using this drug.

    Other SERM drugs are in clinical trials.

    Aromatase inhibitors and inactivators

    Aromatase inhibitors (anastrozole, letrozole) and inactivators (exemestane) may reduce the risk of recurrent and new breast cancer in women with a history of breast cancer.Aromatase inhibitors may also reduce the risk of breast cancer in women with:

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

    Women with an increased risk of breast cancer may have their total body estrogen reduced with an aromatase inhibitor.Before menopause, estrogen is produced by the ovaries and other tissues in a woman’s body, including the brain, adipose tissue, and skin.After menopause, the ovaries stop producing estrogen, but other tissues do not stop producing it.Aromatase inhibitors can be used to block the action of all estrogen-producing aromatases in the body.Aromatase inactivators prevent the enzyme from working.

    Possible damage from the use of aromatase inhibitors includes muscle and joint pain, osteoporosis, hot flashes, and feelings of fatigue.

    Risk-reducing mastectomy

    Some women at high risk for breast cancer may choose a type of mastectomy (removal of both breasts in the absence of signs of breast cancer) that reduces their risk of cancer. These women have a much lower risk of developing breast cancer, and most have fewer concerns about their risk of developing breast cancer. However, it is important to have a cancer risk assessment and to consult about the different approaches to breast cancer prevention before making this decision.

    Ovarian depot

    Most of the body’s estrogen is produced by the ovaries.Treatments used to suppress or reduce estrogen production by the ovaries include oophorectomy, radiation therapy, and the use of certain medications.This is called ovarian denervation.

    Premenopausal women who have an increased risk of breast cancer due to certain changes in the BRCA1 and BRCA2 genes may choose risk-reducing oophorectomy (removal of both ovaries in the absence of signs of breast cancer).This reduces the amount of estrogen in the body and lowers the risk of breast cancer.Reduced-risk ovariectomy may also reduce the increased risk of breast cancer in premenopausal women due to breast radiation.However, it is very important to have a breast cancer risk assessment and counseling before making this decision.A sudden drop in estrogen levels may lead to the onset of menopausal symptoms.These symptoms include hot flashes, sleep disturbances, anxiety and depression.Long-term effects include decreased sex drive, vaginal dryness, and decreased bone density.

    Adequate exercise

    Women who exercise 4 hours or more per week have a lower risk of developing breast cancer.The effect of exercise on breast cancer risk was greatest for women who were normal weight or thin before menopause.

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

    Hormonal contraceptives

    Hormonal contraceptives contain estrogen, or both estrogen and progestin. Some studies suggest that women who are current or recent users of hormonal contraceptives may have a slightly increased risk of breast cancer. Other studies have not shown an increased risk of breast cancer in women who use hormonal contraceptives.

    One study showed a mildly increased risk of breast cancer in women who used hormonal contraceptives for a long time. Another study showed that when women stopped using hormonal contraceptives, the risk of breast cancer decreased with time off the pill.

    More research is needed to clarify whether hormonal contraceptives affect a woman’s risk of breast cancer.

    Environment

    No studies have confirmed whether exposure to certain substances in the environment increases the risk of breast cancer, such as chemicals.

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

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

  • Miscarriage
  • Changes in diet, such as eating less fat or more fruits and vegetables.
  • Taking vitamins, including fenvalerate (a type of vitamin A).
  • Smoking, including active and passive smoking (secondhand smoke)
  • Use of underarm deodorants or antiperspirants.
  • Taking statins (cholesterol-lowering drugs).
  • Oral or intravenous bisphosphonates (drugs used to treat osteoporosis and hypercalcemia)
  • Altered circadian rhythms (physical, psychological, and behavioral changes influenced primarily by the 24-hour cycle of darkness and light), which may be influenced by working night shifts or the amount of light in the bedroom at night.

    Cancer prevention clinical trials are used to study cancer prevention methods.

    Cancer prevention clinical trials are used to study reducing the risk of developing certain cancers.Some cancer prevention studies are conducted in normal people who have not had cancer but have an increased risk of cancer.Some cancer prevention studies are done in people with cancer to try to prevent new cases of the same type of cancer or to reduce the risk of other types of cancer.Other trials are conducted in healthy volunteers without any cancer risk factors.

    Some cancer prevention clinical trials are designed to clarify whether measures people take can prevent cancer.These measures include getting more exercise, quitting smoking, or taking certain medicines, vitamins, minerals, or food supplements.

    New ways to prevent breast cancer are being studied in clinical trials.

    Information about clinical trials supported by the National Cancer Institute (NCI) can be found on the NCI Clinical Trials search page.Clinical trials supported by other organizations can be found on the ClinicalTrials.gov website.