Breast cancer risk factors

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Soroush Seifirad, M.D.[2] Mirdula Sharma, MBBS [3]

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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 alcohol.

Common Risk Factor

• Although less than 15 percent of women with breast cancer have a positive family history, a woman’s risk of breast cancer nearly doubles if she has a first-degree relative (mother, sister, daughter) with the history of breast cancer.
• Around 5-10 percent of breast cancers are due to inherited gene mutations either from one’s mother or father.
• BRCA1 and BRCA2 mutations are the most common genetic abnormality in breast cancer.

• Women with a BRCA1 and BRCA2 mutation have up to a 72% and 69% lifetime risk of developing breast cancer respectively.
• Patients with BRCA1 or BRCA2 are often younger compared to their counterparts without these mutations.
• There is also an increased risk of developing ovarian cancer risk in subjects with mutated BRCA1 and 2.
• Although BRCA1 mutations are barely correlated to breast cancer in men, a 6.8% increased risk of developing breast cancer has been observed in men with BRCA2 mutations.

• We should keep in mind that around 85% of women with breast cancers have no family history.

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 the first pregnancy late in life
• Take postmenopausal hormones (HRT)
• 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.
• Serial mammography might slightly increase the risk of developing breast cancer in high-risk patients such as patients with a family history of breast cancer and patients with known genetic carcinogenic mutations.

• According to a recently published study by Jansen-van der Weide et.al. average increased the risk of breast cancer because of low-dose radiation exposure was 1.5 times higher than that of high-risk women not exposed to low-dose radiation.
• High-risk women exposed before age 20 or with five or more exposures were 2.5 times more likely to develop breast cancer compared to the high-risk women whom were not exposed to low-dose radiation.
• They recommend careful approach in these subgroup of patients, and if possible other diagnostic approaches are better options for these subjects.
• According to another study by Diana L. Miglioretti et.al. radiation-induced breast cancer incidence and mortality from digital mammography screening are impacted by:
• Dose variability from screening and resultant diagnostic work-up,

• Initiation age
• Screening frequency.
• Women with large breasts may be at higher risk of radiation-induced breast cancer;

• However, we should keep in mind that "the benefits of screening outweigh these risks".

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 the 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.