Distant Family History
Breast cancer in non-first degree relatives, such as aunts, grandmothers and cousins, can slightly elevate your breast cancer risk, though not nearly to the extent that breast cancer in a mother, sister or daughter does.
Hormone Replacement Therapy (HRT)
Long-term use of combined estrogen and progesterone (hormone replacement therapy, or HRT) increases the risk of breast cancer. The level of risk appears to return to normal after discontinuing HRT for five years or more.
Previous Benign Breast Biopsy
Women who have had biopsies showing any of the following have a slightly increased risk: fibroadenomas with complex features, hyperplasia without atypia, sclerosing adenosis, and papilloma.
Early Menstruation and Late Menopause
Women who have gone through more menstrual cycles than average because they began menstruating before the age of 12 and/or went through menopause after the age of 55 face a slightly elevated risk.
Delayed Childbirth, or Not Having Children
Having your first child after age 35 or never having children puts you at slightly higher risk. The reason may be similar to the reason early menstruation and late menopause raise the risk: by increasing your exposure to the hormones estrogen and progesterone through more lifetime menstrual cycles.
Alcohol consumption (more than seven drinks a week) has been linked to increased breast cancer risk, particularly before the age of 30. Compared with nondrinkers, women who consume, on average, more than one alcoholic drink a day have a very small increase in risk, and those who consume two to five drinks daily have about 1.5 times the risk of women who drink no alcohol. For these women, reducing alcohol intake can help to lower the risk.
Having dense breast tissue may slightly increase the risk for breast cancer, and can also make the cancer more difficult to detect on mammograms.
The insulin resistance characteristic of diabetes is also believed to raise the risk of breast cancer.
A sedentary lifestyle, particularly before the age of 40, may increase your breast cancer risk. Regular exercise can reduce the risk.
Exposures to some chemicals and pesticides are thought to increase the risk for cancer in general, though the level of this risk is not well understood.
Other Cancer in the Family
A family history of cancer of the ovaries, cervix, uterus, or colon may increase your breast cancer risk slightly.
Female descendents of Eastern and Central European Jews (Ashkenazi) may be at increased risk because inherited alterations in BRCA1 and BRCA2 genes are more common in this population. In the general population, the likelihood of having an alteration in one of the BRCA genes is far less than 1%. In contrast, about 2.3% of individuals who are Ashkenazi Jewish have inherited an alteration in the BRCA genes that significantly increases their risk for breast and ovarian cancer. Alterations in the BRCA genes are also more common in certain other ethnic groups, such as French Canadians and those from Iceland.
Caucasian women are at a slightly higher risk of developing breast cancer than are African-American, Asian, Hispanic, and Native American women, with one exception: Under the age 40, African-American women are more likely to develop breast cancer than Causasian women.