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Breast Cancer Risk Factors

A risk factor is anything that affects your chance of getting a disease, such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs.

But risk factors don’t tell us everything. Having a risk factor, or even several, does not mean that you will get the disease. Most women who have one or more breast cancer risk factors never develop the disease, while many women with breast cancer have no apparent risk factors (other than being a woman and growing older). Even when a woman with risk factors develops breast cancer, it is hard to know just how much these factors may have contributed to her cancer.

There are different kinds of risk factors. Some factors, like a person’s age or race, can’t be changed. Others are linked to cancer-causing factors in the environment. Still others are related personal behaviors, such as smoking, drinking, and diet. Some factors influence risk more than others, and your risk for breast cancer can change over time, due to factors such as aging or lifestyle.

Risk factors you CAN change:

  • postmenopausal obesity
  • use of combined estrogen and progestin menopausal hormones
  • alcohol consumption
  • physical inactivity
  • some environmental exposures

Risk factors you CANNOT change:

Simply being a woman is the main risk factor for developing breast cancer. Although women have many more breast cells than men, the main reason they develop more breast cancer is because their breast cells are constantly exposed to the growth-promoting effects of the female hormones estrogen and progesterone. Men can develop breast cancer, but this disease is about 100 times more common among women than men.

Your risk of developing breast cancer increases as you get older. About 1 out of 8 invasive breast cancers are found in women younger than 45, while about 2 out of 3 invasive breast cancers are found in women age 55 or older.

Genetic risk factors
About 5% to 10% of breast cancer cases are thought to be hereditary, resulting directly from gene defects (called mutations) inherited from a parent.

The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 and BRCA2 genes. In normal cells, these genes help prevent cancer by making proteins that help keep the cells from growing abnormally. If you have inherited a mutated copy of either gene from a parent, you have a high risk of developing breast cancer during your lifetime. The risk may be as high as 80% for members of some families with BRCA mutations. These cancers tend to occur in younger women and are more often bilateral (in both breasts) than cancers in women who are not born with one of these gene mutations. Women with these inherited mutations also have an increased risk for developing other cancers, particularly ovarian cancer.

Although in the U.S., BRCA mutations are found most often in Jewish women of Ashkenazi (Eastern Europe) origin, they can occur in any racial or ethnic group.

Changes in other genes: Other gene mutations can also lead to inherited breast cancers. These gene mutations are much rarer and often do not increase the risk of breast cancer as much as the BRCA genes. They are not frequent causes of inherited breast cancer.

Conditions That Increase Risk

The exact causes of breast cancer are unknown. Research has shown that the following conditions increase a woman’s chances of developing breast cancer:

  • Personal History: Women who have had breast cancer face an increased risk of developing breast cancer again.
  • Family History: The risk for developing breast cancer increases if immediate family members (mother, sister or daughter) have had breast cancer, especially at a young age.
  • Certain Breast Changes: A diagnosis of atypical hyperplasia or lobular carcinoma in situ (LCIS) may increase a woman’s risk for getting breast cancer.
  • Genetic Alterations: Changes in certain genes increase a woman’s risk of developing breast cancer.
  • Estrogen: There is evidence suggesting that the longer a woman is exposed to estrogen (estrogen made by the body, taken as a drug or delivered by a patch) the more likely she is to develop breast cancer.
  • Late Childbearing: Women who have their first child later (after about age 30) have a greater risk of developing breast cancer than women who have their children at a younger age.
  • Breast Density: Breasts that have a more lobular and ductal tissue appear dense on mammograms. Breast cancer develops more in lobular or ductal tissue (not fatty tissue).
  • Radiation Therapy: Women whose breasts have been exposed to radiation during radiation therapy before age 30.
  • Alcohol: Some studies suggest a slightly higher risk of breast cancer among women who consume alcohol.
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