Risk & Detection

What Are The Risk Factors For Breast Cancer?

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 might 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. Some are related to personal behaviors such as smoking, drinking, and diet. Still others are linked to cancer-causing factors in the environment. 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 changes.

Breast Cancer Risk Factors You Cannot Change

  • Gender – Simply being a woman is the main risk factor for developing breast cancer. Men can develop breast cancer, but this disease is about 100 times more common among women than men. This is probably because men have less of the female hormones estrogen and progesterone, which can promote breast cancer cell growth.
  • Aging – our 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 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.
  • BRCA1 and BRCA2 – 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 more often affect 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.
    If you are considering genetic testing, it is strongly recommended that first you talk to a genetic counselor, nurse, or doctor qualified to explain and interpret the results of these tests. It is very important to understand what genetic testing can and can’t tell you, and to carefully weigh the benefits and risks of genetic testing before these tests are done. Testing is expensive and might not be covered by some health insurance plans.
     
  • Family history of breast cancer ~
    • Breast cancer risk is higher among women whose close blood relatives have this disease.
    • Having a first-degree relative (mother, sister, or daughter) with breast cancer almost doubles a woman’s risk.
    • Having 2 first-degree relatives increases her risk about 3-fold.
    • Although the exact risk is not known, women with a family history of breast cancer in a father or brother also have an increased risk of breast cancer.
      Overall, less than 15% of women with breast cancer have a family member with this disease. This means that most (85%) women who get breast cancer do not have a family history of this disease.
  • Personal history of breast cancer ~ A woman with cancer in one breast has a 3- to 4-fold increased risk of developing a new cancer in the other breast or in another part of the same breast. This is different from a recurrence (return) of the first cancer.
  • Race and ethnicity ~ Overall, white women are slightly more likely to develop breast cancer than are African-American women, but African-American women are more likely to die of this cancer. In women under 45 years of age, however, breast cancer is more common in African-American women. Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.
  • Dense breast tissue ~ Women with denser breast tissue (as seen on a mammogram) have more glandular tissue and less fatty tissue, and have a higher risk of breast cancer. Unfortunately, dense breast tissue can also make it harder for doctors to spot problems on mammograms.
  • Certain benign breast conditions ~ Women diagnosed with certain benign breast conditions may have an increased risk of breast cancer. Some of these conditions are more closely linked to breast cancer risk than others. Doctors often divide benign breast conditions into 3 general groups, depending on how they affect this risk.
  1. Non-proliferative lesions: These conditions are not associated with overgrowth of breast tissue. They do not seem to affect breast cancer risk, or if they do, it is to a very small extent.
  2. Proliferative lesions without atypia: These conditions show excessive growth of cells in the ducts or lobules of the breast tissue. They seem to raise a woman’s risk of breast cancer slightly (1 ½ to 2 times normal).
  3. Proliferative lesions with atypia: In these conditions, there is excessive growth of cells in the ducts or lobules of the breast tissue, with some of cells no longer appearing normal. They have a stronger effect on breast cancer risk, raising it 3½ to 5 times higher than normal.
  • Hyperplasia ~ Women with a family history of breast cancer and either hyperplasia or atypical hyperplasia have an even higher risk of developing a breast cancer.
  • Lobular carcinoma in situ ~ In lobular carcinoma in situ (LCIS) cells that look like cancer cells are growing in the lobules of the milk-producing glands of the breast, but they do not grow through the wall of the lobules. LCIS (also called lobular neoplasia) is sometimes grouped with ductal carcinoma in situ (DCIS) as a non-invasive breast cancer, but it differs from DCIS in that it doesn’t seem to become invasive cancer if it isn’t treated. Women with lobular carcinoma in situ (LCIS) have a 7- to 11-fold increased risk of developing cancer in either breast.
  • Menstrual periods ~ Women who have had more menstrual cycles because they started menstruating early (before age 12) and/or went through menopause later (after age 55) have a slightly higher risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the hormones estrogen and progesterone.
  • Previous chest radiation ~ Women who as children or young adults were treated with radiation therapy to the chest area for another cancer (such as Hodgkin disease or non-Hodgkin lymphoma) have a significantly increased risk for breast cancer. This varies with the patient’s age when they got the radiation. If chemotherapy was also given, it might have stopped ovarian hormone production for some time, lowering the risk. The risk of developing breast cancer from chest radiation is highest if the radiation was given during adolescence, when the breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk.

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