In 1940, the lifetime risk of a woman developing breast cancer was 5%, or one in 20. In 2015 (the latest year for which statistics are available), the risk was just over 12% -- or more than one in 8. In many cases, it's not known why a woman gets breast cancer.
What Are the Risk Factors for Breast Cancer?
A risk factor is anything that increases a person's chance of getting a disease. Different cancers have different risk factors.
However, having a cancer risk factor, or even several of them, does not necessarily mean that a person will get cancer. Some women with one or more breast cancer risk factors never develop breast cancer, while about half of women with breast cancer have no apparent risk factors.
Significantly higher risk
- History. A woman with a history of cancer in one breast, such as ductal carcinoma in situ (DCIS) or invasive breast cancer, is three to four times likelier to develop a new breast cancer, unrelated to the first one, in either the other breast or in another part of the same breast. This is different than a recurrence of the previous breast cancer.
- Age. Your risk for breast cancer increases as you age. About 80% of women diagnosed with breast cancer each year are ages 45 or older, and about 43% are ages 65 or above. Consider this: In women ages 40 to 50, there is a one in 68 risk of developing breast cancer. From ages 50 to 60, that risk increases to one in 42. In the 60 to 70 age group, the risk is one in 28. In women ages 70 and older, one in 26 is at risk of developing the disease.
Moderately higher risk
- Direct family history. Having a mother, sister, or daughter ("first-degree" relative) who has breast cancer puts a woman at higher risk for the disease. The risk is even greater if this relative developed breast cancer before menopause and had cancer in both breasts. Having one first-degree relative with breast cancer approximately doubles a woman's risk, and having two first-degree relatives triples her risk.
- Having a male blood relative with breast cancer will also increase a woman's risk of the disease.
- Genetics. About 5% to 10% of breast cancer cases are thought to be hereditary. Carriers of alterations in either of two familial breast cancer genes called BRCA1 or BRCA2 are at higher risk. Women with an inherited alteration in the BRCA1 gene have about a 72% chance of developing breast cancer by age 80, and those with an inherited alteration in the BRCA2 gene have about a 69% chance of developing breast cancer. There are several other types of abnormal genes that increase risk of breast cancer.
- Breast lesions. A previous breast biopsy result of atypical hyperplasia (lobular or ductal) or lobular carcinoma in situ increases a woman's breast cancer risk by four to five times.
Slightly higher risk
- Distant family history. This refers to breast cancer in second- or third-degree relatives such as aunts, grandmothers, and cousins.
- Previous abnormal breast biopsy. Women with earlier biopsies showing any of the following have a slight increased risk: fibroadenomas with complex features, hyperplasia without atypia, sclerosing adenosis, and solitary papilloma.
- Age at childbirth . Having your first child after age 35 or never having children puts you at higher risk.
Early menstruation . Longer lifetime exposure to endogenous (your own) estrogen increases your risk, such as starting to menstruate before age 12, starting menopause after age 55, and never having had a pregnancy.
- Weight . Being overweight (especially in the waist), with excess caloric and fat intake, increases your risk, especially after menopause.
- Excessive radiation . This is especially true for women who were exposed to a large amount of radiation before age 30 -- usually as treatment for cancers such as lymphoma.
- Other cancer in the family. If a family member had ovarian cancer under age 50, your risk is increased.
- Heritage. Female descendants of Eastern and Central European Jews (Ashkenazi) are at increased risk.
- Alcohol. Use of alcohol is linked to increased risk of developing breast cancer. Compared with nondrinkers, women who consume one alcoholic drink a day have a very small increase in risk, and those who have 2 to 5 drinks daily have about 1.5 times the risk of women who do not drink.
- Race. Caucasian women are at a slightly higher risk of developing breast cancer than are African-American, Asian, Hispanic, and Native American women. The exception to this is African-American women, who are more likely than Caucasians to have breast cancer under age 40.
- Hormone Replacement Therapy (HRT). Long-term use of combined estrogen and progesterone increases the risk of breast cancer. This risk seems to return to that of the general population after discontinuing them for five years or longer.
- Less lifetime exposure to endogenous estrogen. Having a pregnancy before age 18, starting menopause early, and having the ovaries removed before age 37 decreases the risk of developing breast cancer.
Factors not related to breast cancer
- Fibrocystic breast changes
- Multiple pregnancies
- Coffee or caffeine intake
- Use of anti-perspirants
- Wearing underwire bras
- Using hair dye
- Having an abortion or miscarriage
- Using breast implants
Scientists are still investigating whether smoking, high-fat diets, lack of exercise, and environmental pollution increase breast cancer risk. Some studies have suggested that women who are using birth control pills have a very slight increased risk of developing breast cancer. That risk disappears after stopping them for 10 years or more. Still other studies show no relation. More research is under way to confirm these findings.
Women who breastfeed have a reduced risk of breast cancer.