Breast Cancer Causes

Certain risk factors increase the likelihood that a person will develop breast cancer. Having one or more risk factors, however, doesn't mean that a person will get the disease. Being female and getting older are two risk factors for breast cancer; yet many older women never get breast cancer.

Breast cancer risk factors are not all equal. A family history of breast cancer increases a person's risk more than using oral contraceptives. Moreover, uncontrollable risk factors such as being female cannot be changed, while people can avoid controllable risk factors such as the long-term use of hormone replacement therapy.

Uncontrollable risk factors

Healthcare providers can describe screening and preventative options for people with the following uncontrollable breast cancer risk factors:

Sex

Being female increases a person's risk of breast cancer. Women develop breast cancer 100 times more often than men.

Age

The risk of getting breast cancer increases with advancing age. Approximately 80% of breast cancer cases occur in women over age 50. Breast cancer in men usually occurs after age 60.

Race

Breast cancer in African American women is more aggressive biologically than in other races. African American women are more likely to have a hard-to-treat form of breast cancer, get it earlier, and are less likely to survive.

Genes

Women in families with a high incidence of breast cancer sometimes decide to be tested for gene defects (mutations) that increase a person's risk of breast cancer. The most common inherited defects occur in the BRCA1 and BRCA2 genes. Other rare gene defects associated with breast cancer include the ATM gene, the CHEK-2 gene, and the p53 tumor suppressor gene.

Personal history of breast cancer

Breast cancer in one breast increases a person's risk of getting a new cancer in another part of the same breast or in the other breast.

Family history of breast cancer

People are at increased risk of breast cancer if a close blood relative has had breast cancer. A women's risk doubles if her mother, sister, or daughter has had breast cancer.

Benign breast conditions

Benign (noncancerous) breast conditions are very common, may be uncomfortable, but are not life threatening. The most common benign breast conditions are:

Fibrocystic change (dense, irregular, and lumpy breasts)
Benign breast tumors
Breast inflammation

The following benign breast conditions may slightly increase a person's risk of developing breast cancer:

A breast lump or thickening of breast tissue
A pain or a discharge (other than milk) from the nipple
Dense breast tissue in older women

Any breast changes should be reported to a healthcare provider as soon as possible.

Menstrual history

Women who start menstruating early (before age 12) or go through menopause late (after age 55) have an increased risk of breast cancer. The higher risk may be due to their longer exposure to female hormones.

Liver disease

Men with severe liver disease (cirrhosis) often develop gynecomastia (benign male breast growth) and have an increased risk of breast cancer. The condition causes them to have lower levels of androgens (male hormones) and higher levels of estrogens (female hormones).

Klinefelter syndrome

Men with Klinefelter syndrome have more than one X chromosome in addition to their Y chromosome. Men with Klinefelter syndrome have smaller testicles, lower levels of androgens, and higher levels of estrogens. They often develop gynecomastia and may have a slight risk of breast cancer.

Controllable risk factors

Healthcare providers may be able to suggest ways to avoid the following controllable breast cancer risk factors:

Childbirth and breastfeeding

Women who have never had children or had a first child after age 30 have an increased risk of breast cancer. Being pregnant more than once and at an early age reduces a woman's risk of breast cancer. Breast feeding slightly lowers the risk of breast cancer.

Oral contraceptives

Women currently using oral contraceptives may have a slightly greater risk of breast cancer than women who never used the pill, especially if they started using it during their teenage years. Women who stopped using oral contraceptives over 10 years ago do not have any increased risk.

Oral contraceptive use has also been shown to:

Increase the risk of cervical and liver cancer.
Decrease the risk of ovarian and endometrial cancer.

Hormone replacement therapy for women

Long-term use (several years or longer) of hormone replacement therapy (HRT) containing both estrogen and progestin (synthetic progesterone) increases the risk of breast cancer. HRT containing estrogen alone does not increase the risk of breast cancer in women without an intact uterus due to a hysterectomy.

After five years of stopping HRT, a woman's risk of breast cancer risk returns to normal.

Hormone therapy for men

Some men with prostate cancer are treated with hormone therapy containing estrogen. Although this treatment may slightly increase their risk of breast cancer, the risk is small compared to the risk of not treating their prostate cancer.

Higher doses of estrogens are taken by men undergoing a sex change procedure and put them at a much greater risk of breast cancer.

DES

The drug diethylstilbestrol (DES), a synthetic form of estrogen, was given to pregnant women from 1938 to 1971 to prevent miscarriage. These women may have a slightly increased risk of breast cancer.

Radiation therapy to the chest

People treated with radiation therapy to the chest before age 30 have an increased risk of breast cancer. People treated at a younger age have an even greater risk.

Alcohol use

Drinking more than 1 to 2 glasses of alcohol a day increases a person's risk of breast cancer.

Obesity

Being overweight or obese appears to increase the risk of breast cancer, especially after menopause. Obesity also causes men to produce higher levels of estrogens, which increases their risk of breast cancer.

Physical inactivity

People who are physically inactive throughout their lives appear to have an increased risk of breast cancer and exercise may provide some modest reduction in a person's risk of breast cancer.

Suspected risk factors

The following suspected breast cancer risk factors are under study:

Cigarette smoking and secondhand smoke
Dietary additives and contaminants
Environmental pollutants, such as pesticides and polychlorinated biphenyl (PCBs)

Non-risk factors

The following factors have not been shown to increase a person's risk of breast cancer:

Breast implants
Induced abortions and miscarriages
Underarm antiperspirants and deodorants
Wearing underwire bras
Working at night

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