Breast cancer risk factors

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Mirdula Sharma, MBBS [2]

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Overview

Common risk factors in the development of breast cancer are family history, dense breast, obesity, radiation therapy, older age at first birth or never having given birth, hormone replacement therapy, and alchohol.

Common Risk Factor

• A woman’s risk of breast cancer nearly doubles if she has a first-degree relative (mother, sister, daughter) who has been diagnosed with breast cancer. Less than 15% of women who get breast cancer have a family member diagnosed with it.
• About 5-10% of breast cancers can be linked to gene mutations inherited from one’s mother or father. Mutations in the BRCA1 and BRCA2 genesare the most common. On average, women with a BRCA1 mutation have up to a 72% lifetime risk of developing breast cancer. For women with a BRCA2 mutation, the risk is 69%. Breast cancer that is positive for the BRCA1 or BRCA2 mutations tends to develop more often in younger women. An increased ovarian cancer risk is also associated with these genetic mutations. In men, BRCA2 mutations are associated with a lifetime breast cancer risk of about 6.8%; BRCA1 mutations are a less frequent cause of breast cancer in men.
• About 85% of breast cancers occur in women who have no family history of breast cancer. These occur due to genetic mutations that happen as a result of the aging process and life in general, rather than inherited mutations

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A personal history of breast cancer or benign (noncancer) breast disease

• Women with any of the following have an increased risk of breast cancer:

• A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
• A personal history of benign (noncancer) breast disease.

A family history of breast cancer

• Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.

Inherited gene changes

• Women who have inherited changes in the BRCA1 and BRCA2 genes or in certain other genes have a higher risk of breast cancer, ovarian cancer, and maybe colon cancer. The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.
• Men who have inherited certain changes in the BRCA2 gene have a higher risk of breast, prostate, and pancreatic cancers, and lymphoma.

Dense breasts

• Having breast tissue that is dense on a mammogram is a factor in breast cancer risk. The level of risk depends on how dense the breast tissue is. Women with very dense breasts have a higher risk of breast cancer than women with low breast density.
• Increased breast density is often an inherited trait, but it may also occur in women who have not had children, have a first pregnancy late in life, take postmenopausal hormones, or drink alcohol.

Exposure of breast tissue to estrogen made in the body

• Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.
• A woman's exposure to estrogen is increased in the following ways:

• Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
• Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
• Older age at first birth or never having given birth: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.

Taking hormone therapy for symptoms of menopause

• Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.

Radiation therapy to the breast or chest

• Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given. The risk is highest if radiation treatment was used during puberty, when breasts are forming.
• Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.
• For women who have inherited changes in the BRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.

Obesity

• Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.

Drinking alcohol

• Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.

Less Common Risk Factors

Tobacco

• Most studies have not found an increased risk of breast cancer from active tobacco smoking, although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to secondhand smoke compared to women who reported no exposure to secondhand smoke.

Radiation

• Women who have received high-dose ionizing radiation to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.

Impact of environmental estrogenic mimics

• Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds, including chemicals used in pesticides, cosmetics and cleaning products, contribute to the development of breast cancer.
• A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.

The increasing prevalence of these substances in the environment may explain the rising incidence of breast cancer, though direct evidence is sparse.

Dioxins

• Although not well-quantified, there has long been a concern about risk associated with environmental estrogenic compounds, such as dioxins.

Light levels

• Researchers at the National Cancer Institute and National Institute of Environmental Health Sciences have conducted a study that suggests that artificial light during the night can be a factor for breast cancer.