Although no one knows exactly why breast cancer develops, most experts believe it is caused by a combination of genetic and environmental factors. While some people may have certain risk factors and never develop the disease, others may develop the disease but not have any known risk factors.
Genetic Factors
Environmental Factors
Genetic Factors
Just as there are genes that define traits such as eye and hair color, there are also genes that increase a person's susceptibility to diseases such as cancer.
In some cases, doctors know specifically which genes are mutated or not functioning properly and cause cancer in a person's family. In other cases the specific genes involved have not yet been identified, and doctors only know that breast cancer runs in a person's family.
The two genes most often associated with inherited breast cancer — BRCA1 and BRCA2 — are believed to account for 5 to 10 percent of all cases of breast cancer. Mutations in these two genes also increase a woman's risk of other cancers, especially ovarian cancer.
By learning whether you have a genetic risk for breast cancer, you may learn that you should be considering different screening and prevention options from those appropriate for the general population. You may also learn information that helps other family members understand their cancer risk.
Environmental Factors
Nongenetic factors that may increase a person's risk for breast cancer include:
- Increasing age
- Exposure to radiation
- Hormone replacement therapy
- First childbirth after age 30
- Early onset of menstruation
- Late menopause
- Obesity (especially after menopause)
- A high-fat diet
- Excessive alcohol consumption
- Personal history of breast biopsies or breast disease
When thinking about your risk for developing breast cancer, keep in mind that there is no one factor that can predict who will develop breast cancer. There are risk factors, however, over which you may have influence (such as diet).
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