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 andBRCA2genes, 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 increases the risk of breast cancer in postmenopausal women who have not used hormone replacement therapy.
Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.
Women who have inherited certain changes in the BRCA1 and BRCA2genes 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.
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.