What Is Cancer Prevention? Cancer prevention is action taken to lower the chance of getting cancer. By preventing cancer, the number of new cases of cancer in a group or population is lowered. Hopefully, this will lower the number of deaths caused by cancer. When studying ways to prevent cancer, scientists look at risk factors and protective factors. Anything that increases your chance of developing cancer is called a cancer risk factor. Anything that decreases your chance of developing cancer is called a cancer protective factor. Risk Factors Some risk factors for cancer can be avoided, but many cannot. For example, both smoking and inheriting certain genes are risk factors for some types of cancer, but only smoking can be avoided. Regular exercise and a healthy diet may be protective factors for some types of cancer. Avoiding risk factors and increasing protective factors may lower your risk but it does not mean that you will not get cancer. Different ways to prevent cancer are being studied, including - changing lifestyle or eating habits  - avoiding things known to cause cancer  - taking medicine to treat a precancerous condition or to keep cancer from starting.  changing lifestyle or eating habits avoiding things known to cause cancer taking medicine to treat a precancerous condition or to keep cancer from starting. (For more on risk factors, see the chapter on "Risk Factors.") Here are protective factors for breast cancer. Less Exposure to Estrogen Decreasing the length of time a woman's breast tissue is exposed to estrogen may help lower her risk of developing 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.  -  Surgical removal of the ovaries.  The ovaries make estrogen. The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries. Also, drugs may be taken to lower the amount of estrogen made by the ovaries.  -  Late menstruation. Menstrual periods that start at age 14 or older decreases the number of years the breast tissue is exposed to estrogen.  - Early menopause. The fewer years a woman menstruates, the shorter the time her breast tissue is exposed to estrogen.   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.  Surgical removal of the ovaries.  The ovaries make estrogen. The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries. Also, drugs may be taken to lower the amount of estrogen made by the ovaries. Late menstruation. Menstrual periods that start at age 14 or older decreases the number of years the breast tissue is exposed to estrogen. Early menopause. The fewer years a woman menstruates, the shorter the time her breast tissue is exposed to estrogen. 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. Learn more about the benefits of exercise for older adults.  For exercises tailored to older adults, visit Go4Life, the exercise and physical activity campaign from the National Institute on Aging (NIA) at NIH. 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. Learn about menopausal hormone therapy and cancer. Selective Estrogen Receptor Modulators (SERMs) 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 or raloxifene lowers the risk of breast cancer in postmenopausal women. Tamoxifen also lowers the risk of breast cancer in high-risk premenopausal women. With either drug, the reduced risk lasts for several years after treatment is stopped. Lower rates of broken bones have been noted in patients taking raloxifene. Prophylactic Mastectomy Some women who have a high risk of breast cancer may choose to have a prophylactic 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 cancer risk assessment and counseling about the different ways to prevent breast cancer before making this decision.  Learn more about surgery to reduce the risk of breast cancer. Prophylactic Oophorectomy 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 prophylactic 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. Prophylactic 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 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. Unclear As Risk Factors It is not clear whether the following affect the risk of breast cancer. - Oral contraceptives. Taking oral contraceptives ("the pill") may slightly increase the risk of breast cancer in current users. This risk decreases over time. Some oral contraceptives contain estrogen. Progestin-only contraceptives that are injected or implanted do not appear to increase the 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.  Oral contraceptives. Taking oral contraceptives ("the pill") may slightly increase the risk of breast cancer in current users. This risk decreases over time. Some oral contraceptives contain estrogen. Progestin-only contraceptives that are injected or implanted do not appear to increase the 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. For More Information Clinical trials are taking place in many parts of the country. Information about clinical trials can be found at  http://www.cancer.gov/clinicaltrials on the website of the National Cancer Institute (NCI). Check NCI's list of cancer clinical trials for breast cancer prevention trials that are now accepting patients.