| General Risk Factors
Age
The older a woman becomes the more likely she is to develop
breast cancer. For example, the incidence of breast cancer
in women 80-85 years old is 15 times higher than it is
in women who are 30-35 years old. Approximately 77%
of the breast cancers diagnosed are found in women who
are
at
least 50
years old.1
Personal History of Breast Cancer
According to the American Cancer Society, women who have had breast cancer in the past face a 3-4 times greater risk of developing breast cancer in another area of the same breast or in their other breast. This risk pertains to developing a new breast cancer, not a recurrence.
Family History
Approximately 5-10% of all breast cancers are hereditary. The National Cancer Institute defines a family history of breast cancer as a first-degree relative (mother, daughter, sister) or 2 or more close relatives who have had breast cancer. The risk is higher if the relative(s) developed breast cancer in both breasts, or developed breast cancer before menopause.
Genetics
In recent years, researchers have found that abnormal changes (known as "mutations") in genes called BRCA1 and BRCA2 cause some women to be more likely to develop breast cancer and ovarian cancer. Women with the BRCA1 or BRCA2 mutation are believed to have a 55-85% chance of developing breast cancer by the age of 70. These genetic mutations appear in less than 1% of the general population.
Atypical Cells
Atypical cells are abnormal cells inside the milk ducts. Atypical cells do not necessarily progress to cancer. However, we do know that atypical cells increase risk. The presence of atypical cells has been shown to increase a woman's breast cancer relative
risk 4-5 times compared to a woman without atypical cells.2-4 For women who already have a family history, the presence of atypical cells increases their risk even further compared to women who do not have a family history or atypical cells.
Hormone-Related Risk Factors
Research suggests that estrogen affects breast cancer risk. Estrogen is a hormone all women start to produce when menstruation begins. Women continue to produce estrogen until they reach menopause. Estrogen itself doesn't cause breast cancer, but it may help encourage the growth and multiplication of cancerous cells. The following factors affect estrogen levels in the body, and are thought to increase breast cancer risk.
- First menstrual period occurring before age 12
- First full term pregnancy after the age of 30
- No live births
- Menopause that starts after age 54
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