Virginia Commonwealth University

VCU Massey Cancer Center

Causes, risk factors and genetics

Risk factors for breast cancer

Any woman may develop breast cancer. However, the following risk factors may increase the likelihood of developing the disease.

Risk factors that cannot be changed:

  • Gender.
    Breast cancer occurs nearly 100 times more often in women than in men.
  • Aging.
    A majority of cases occur after age 50.
  • Personal history of breast cancer.
  • Previous breast irradiation.
  • Family history and genetic factors.
    Having a close relative, such as a mother or sister, with breast cancer increases the risk. This factor includes changes in certain genes such as BRCA1, BRCA2 and others.
  • Benign breast disease.
  • Previous breast biopsy in which the tissue showed hyperplasia with or without atypia (atypia is associated with a greater risk than hyperplasia without atypia).
  • Menstrual periods that began early in life (before age 12).
  • Menopause that began later in life (after age 55).

The most frequently cited lifestyle-related risk factors:

  • Smoking.
  • Not having children, or first child after age 30.
  • Oral contraceptives.
    In particular, women who took oral contraceptives before 1995 will have a higher risk due to the higher dosages used in contraceptives before then.
  • Obesity and possibly a high-fat diet (more studies needed).
  • Physical inactivity.
  • Alcohol (greater risk if two to five drinks per day).
  • Long-term, post-menopausal use of combined estrogen and progestin hormone replacement therapy (HRT).
  • Weight gain and obesity after menopause.

Environmental risk factors:

  • Exposure to pesticides or other chemicals is currently being examined as a possible risk factor, including women with who received diethylstibestrol.

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About risk factors

Although there are some women who are at higher risk, the fact is all women are at risk for breast cancer. That is why it is so important to follow the three-step plan for breast health. Early detection of problems provides the greatest possibility of successful treatment.

Some people with one or more risk factors never develop a disease, such as cancer, while others develop cancer and have no known risk factors.

Although certain factors may suggest or define a person’s possible risks, they do not necessarily cause the disease.

Different diseases, including cancers, have different risk-factor lists. When reading about risk factors for breast cancer, keep in mind that the word “risk” is used in different ways.

Lifetime risk refers to the probability that a person, over the course of his or her lifetime, will be diagnosed or die from cancer.

Over her lifetime, a woman in the U.S. has a one-in-eight risk of developing breast cancer, and a one-in-28 risk of dying from breast cancer.

Relative risk is a measure of the strength of the relationship between risk factors and cancer.

With respect to breast cancer, it compares the risk of developing breast cancer in women who have a certain trait or exposure to women who do not have the trait or exposure.

For example, women who have a family history of breast cancer are about 100 percent more likely to develop breast cancer than women who do not have a family history.

Source: National Cancer Institute

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The genetics of breast cancer

If breast cancer runs in your family, contact Massey’s familial genetic counseling program to see if you should be tested. If you have questions or would like to discuss your situation, please contact:

The lifetime risk for a woman to develop breast cancer is 12.8 percent or one in eight, while the lifetime risk to develop ovarian cancer is a little greater than 1 percent (1.4 percent, or one in 70). Breast cancer occasionally occurs in men.

Approximately 5 percent to 10 percent of breast cancers are due to known predisposing genetic factors, meaning that the majority of breast cancers are, in fact, not inherited. Consider the statistics below.

  • Of those cases of breast cancer that are inherited:
    • 20 percent to 40 percent are due to mutations in the BRCA1 gene.
    • 10 percent to 30 percent are due to mutations in the BRCA2 gene.
    • Less than 1 percent are due to mutations in the P53 gene.
    • Less than 1 percent are due to mutations in the PTEN gene.
    • 30 percent to 70 percent are due to other gene mutations.

There are several genetic syndromes associated with an increased risk for breast cancer that require clinical care by a physician or other health care professional. Listed in the directory below are some for which we have provided a brief overview.

The genetics of breast and ovarian cancer

Hereditary breast ovarian cancer syndrome has several distinct characteristics. Please visit the page below for more information on the BRCA1 and BRCA2 genes.

Hereditary Breast Ovarian Cancer Syndrome (BRCA1 / BRCA2)