What is 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.
To prevent new cancers from starting, 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.
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 medicines to treat a precancerous condition or to keep cancer from starting.
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, eating a healthy diet,
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 risk factors may increase the risk of breast cancer:
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.
- Late menopause: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
- Late pregnancy or never being pregnant: 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.
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 progesterone
or progestin. This type of HRT/HT increases the risk of breast cancer.
Women taking combination HRT/HT also may be more likely to have an abnormal mammogram. Studies show that when women stop taking estrogen combined with progesterone, the risk of breast cancer decreases.
Exposure to Radiation
Radiation therapy to the chest for the treatment of cancers
increases the risk of breast cancer, starting 10 years after treatment
and lasting for a lifetime. The risk of developing 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. For example, radiation therapy used to treat Hodgkin disease by age 16, especially radiation to the chest and neck, increases the risk of breast cancer.
Radiation therapy to treat cancer in one breast does not appear to increase the risk of developing cancer in the other breast.
For women who are at risk of breast cancer due to 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 in postmenopausal women who have not used hormone replacement therapy.
Alcohol
Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.
Inherited Risk
Women who have inherited certain changes in the BRCA1 and BRCA2 genes have a higher risk of breast cancer, and the breast cancer may develop at a younger age.
The following protective factors may decrease the risk of breast cancer:
Estrogen-only hormone therapy for postmenopausal women
Estrogen-only hormone therapy may be given to women who have had a hysterectomy. In these women, estrogen-only therapy after menopause decreases the risk of breast cancer. In women who have a uterus, estrogen-only therapy increases the risk of uterine cancer.
Exercise
Exercising
four or more hours a week may decrease hormone levels and help lower
breast cancer risk. The effect of exercise on breast cancer risk may be
greatest in premenopausal
women of normal or low weight. Care should be taken to exercise safely,
because exercise carries the risk of injury to bones and muscles.
Estrogen (decreased exposure)
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:
- Pregnancy: Estrogen levels are lower during pregnancy. The risk of breast cancer appears to be lower if a woman has her first full-term pregnancy before she is 20 years old.
- Breast-feeding: Estrogen levels may remain lower while a woman is breast-feeding.
- Ovarian ablation: The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries, which make estrogen. Also, drugs may be taken to lower the amount of estrogen made by the ovaries.
- Late menstruation: Beginning to have menstrual periods 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.
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. Protective effects with either drug last
for several years after treatment is stopped. Lower rates of broken
bones have been noted in patients taking raloxifene.
Taking tamoxifen increases the risk of serious conditions, including endometrial cancer, stroke, cataracts, and blood clots (especially in the lungs,
brain, and legs). The risk of having these conditions increases with
age. 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
conditions decreases after tamoxifen is stopped. Talk with your doctor
about the risks and benefits of taking this drug.
Taking
raloxifene increases the risk of developing 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 at both high risk
and low risk of developing the disease. 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
Aromatase inhibitors
lower the risk of a new breast cancer in women who have an increased
risk of breast cancer. Women with an increased risk of breast cancer
include the following:
- 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 (considers many risk factors for 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.
Possible harms from taking aromatase inhibitors include muscle and joint pain, osteoporosis, hot flashes, and feeling very tired.
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 lowered in these women. However, it is very
important to have a cancer risk assessment and counseling about all options for possible prevention before making this decision. In some women, prophylactic mastectomy may cause anxiety, depression, and concerns about body image.
Prophylactic oophorectomy
Some women who have a high risk of breast cancer 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. 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 onset of symptoms of menopause, including hot flashes, trouble sleeping, anxiety, and depression. Long-term effects include decreased sex drive, vaginal dryness, and decreased bone density. These symptoms vary greatly among women.
Fenretinide
Fenretinide is a type of vitamin A called a retinoid.
When given to premenopausal women who have a history of breast cancer,
fenretinide may lower the risk of forming a new breast cancer. Taken
over time, fenretinide may cause night blindness and skin disorders. Women must avoid pregnancy while taking this drug because it could harm a developing fetus.
The following have been proven not to be risk factors for breast cancer or their effects on breast cancer risk are not known:
Abortion
There does not appear to be a link between abortion and 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. The most commonly used oral
contraceptive contains 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, metals, dust, and pollution) increases the risk of breast cancer.
Diet
Diet
is being studied as a risk factor for breast cancer. It is not proven
that a diet low in fat or high in fruits and vegetables will prevent
breast cancer. For more information on diet and health, see the Nutrition for
Active and passive cigarette smoking
It has not been proven that either active cigarette smoking or passive smoking (inhaling secondhand smoke) increases the risk of developing breast cancer.
Statins
Studies have not found that taking statins (cholesterol -lowering drugs) affects the risk of breast cancer.
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