Breast Cancer Treatment (PDQ®): Treatment - Health Professional Information [NCI] - General Information About Breast Cancer
Anatomy of the female breast. The nipple and areola are shown on the outside of the breast. The lymph nodes, lobes, lobules, ducts, and other parts of the inside of the breast are also shown.
Risk and Protective Factors
Increasing age is the most important risk factor for breast cancer. Other risk factors for breast cancer include the following:
- Family health history.
- Major inheritance susceptibility.[6,7,8]
- Germline mutation of the genes BRCA1 and BRCA2, and other breast cancer susceptibility genes.[9,10,11,12,13]
- Alcohol intake.
- Breast tissue density (mammographic).[15,16]
- Estrogen (endogenous):[17,18,19,20]
- Menstrual history (early menarche/late menopause).[21,22,23]
- Older age at first birth.
- Hormone therapy history:
- Combination estrogen plus progestin hormone replacement therapy (HRT).[25,26,27,28]
- Oral contraception.
- Lack of physical exercise.
- Personal history of breast cancer.
- Personal history of proliferative forms of benign breast disease.[34,35,36,37,38,39,40]
- Radiation exposure to the breast/chest.[43,44]
Age-specific risk estimates are available to help counsel and design screening strategies for women with a family history of breast cancer.[45,46]
Of all women with breast cancer, 5% to 10% may have a germline mutation of the genes BRCA1 and BRCA2. Specific mutations of BRCA1 and BRCA2 are more common in women of Jewish ancestry. The estimated lifetime risk of developing breast cancer for women with BRCA1 and BRCA2 mutations is 40% to 85%. Carriers with a history of breast cancer have an increased risk of contralateral disease that may be as high as 5% per year. Male BRCA2 mutation carriers also have an increased risk of breast cancer.
Mutations in either the BRCA1 or the BRCA2 gene also confer an increased risk of ovarian cancer [50,51] or other primary cancers.[50,51] Once a BRCA1 or BRCA2 mutation has been identified, other family members can be referred for genetic counseling and testing.[52,53,54,55] (Refer to the PDQ summaries on Genetics of Breast and Ovarian Cancer; Breast Cancer Prevention; and Breast Cancer Screening for more information.)