About 5% to 10% of breast cancers are thought to be hereditary, caused by abnormal genes passed from parent to child.

Genes are short segments of DNA (deoxyribonucleic acid) found in chromosomes. DNA contains the instructions for building proteins. And proteins control the structure and function of all the cells that make up your body.

Think of your genes as an instruction manual for cell growth and function. Changes or mistakes in the DNA are like typographical errors. They may provide the wrong set of instructions, leading to faulty cell growth or function. In any one person, if there is an error in a gene, that same mistake will appear in all the cells that contain the same gene. This is like having an instruction manual in which all the copies have the same typographical error.

There are two types of DNA changes: those that are inherited and those that happen over time. Inherited DNA changes are passed down from parent to child. Inherited DNA changes are called germ-line alterations or mutations.

DNA changes that happen over the course of a lifetime, as a result of the natural aging process or exposure to chemicals in the environment, are called somatic alterations.

Some DNA changes are harmless, but others can cause disease or other health issues. DNA changes that negatively affect health are called mutations.

Most inherited cases of breast cancer are associated with mutations in two genes: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two).

Everyone has BRCA1 and BRCA2 genes. The function of the BRCA genes is to repair cell damage and keep breast, ovarian, and other cells growing normally. But when these genes contain mutations that are passed from generation to generation, the genes don't function normally and breast, ovarian, and other cancer risk increases. BRCA1 and BRCA2 mutations may account for up to 10% of all breast cancers, or 1 out of every 10 cases.

Having a BRCA1 or BRCA2 mutation doesn't mean you will be diagnosed with breast cancer. Researchers are learning that other mutations in pieces of chromosomes -- called SNPs (single nucleotide polymorphisms) -- may be linked to higher breast cancer risk in women with a BRCA1 mutation as well as women who didn't inherit a breast cancer gene mutation.

Women who are diagnosed with breast cancer and have a BRCA1 or BRCA2 mutation often have a family history of breast cancer, ovarian cancer, and other cancers. Still, most people who develop breast cancer did not inherit a genetic mutation linked to breast cancer and have no family history of the disease.

You are substantially more likely to have a genetic mutation linked to breast cancer if:

If one family member has a genetic mutation linked to breast cancer, it does not mean that all family members will have it.

The average woman in the United States has about a 1 in 8, or about 12%, risk of developing breast cancer in her lifetime. Women who have a BRCA1 mutation or BRCA2 mutation (or both) can have up to a 72% risk of being diagnosed with breast cancer during their lifetimes. Breast cancers associated with a BRCA1 or BRCA2 mutation tend to develop in younger women and occur more often in both breasts than cancers in women without these genetic mutations.

Women with a BRCA1 or BRCA2 mutation also have an increased risk of developing ovarian, colon, and pancreatic cancers, as well as melanoma.

Men who have a BRCA2 mutation have a higher risk of breast cancer than men who don't -- about 8% by the time they're 80 years old. This is about 80 times greater than average.

Men with a BRCA1 mutation have a slightly higher risk of prostate cancer. Men with a BRCA2 mutation are 7 times more likely than men without the mutation to develop prostate cancer. Other cancer risks, such as cancer of the skin or digestive tract, also may be slightly higher in men with a BRCA1 or BRCA2 mutation.

Mutations in other genes are also associated with breast cancer. These genetic mutations are much less common and don't seem to increase risk as much as BRCA1 and BRCA2 mutations, which are considered rare. Still, because these genetic mutations are even rarer, they haven't been studied as much as the BRCA mutations.

Inheriting two abnormal copies of the BRCA2, BRIP1, MRE11A, NBN, PALB2, RAD50, or RAD51C genes causes the disease Fanconi anema, which suppresses bone marrow function and leads to extremely low levels of red blood cells, white blood cells, and platelets. People with Fanconi anemia also have a higher risk of several other types of cancer, including kidney cancer and brain cancer.

There are genetic tests available to determine if someone has a BRCA1 or BRCA2 mutation. A genetic counselor also may order testing for ATM, CDH1, CHEK2, MRE11A, MSH6, NBN, PALB2, PMS2, PTEN, RAD50, RAD51C, SEC23B, or TP53 mutations, individually or as part of a larger gene panel that includes BRCA1 and BRCA2.

For more information, visit the Breastcancer.org Genetic Testing pages.

If you know you have an abnormal gene linked to breast cancer, there are lifestyle choices you can make to keep your risk as low it can be:

These are just a few steps you can take. Review the links on the left side of this page for more options.

Along with these lifestyle choices, there are other risk-reduction options for women at high risk because of abnormal genetics.

Hormonal therapy medicines: Two SERMs (selective estrogen receptor modulators) and two aromatase inhibitors have been shown to reduce the risk of developing hormone-receptor-positive breast cancer in women at high risk.

Hormonal therapy medicines do not reduce the risk of hormone-receptor-negative breast cancer.

More frequent screening: If you're at high risk because of an abnormal breast cancer gene, you and your doctor will develop a screening plan tailored to your unique situation. You may start being screened when you're younger than 40. In addition to the recommended screening guidelines for women at average risk, a screening plan for a woman at high risk may include:

Women with an abnormal breast cancer gene need to be screened twice a year because they have a much higher risk of cancer developing in the time between yearly screenings. For example, the Memorial Sloan-Kettering Cancer Center in New York, NY recommends that women with an abnormal BRCA1 or BRCA2 gene have both a digital mammogram and an MRI scan each year, about 6 months apart (for example, a mammogram in December and an MRI in June).

A breast ultrasound is another powerful tool that can help detect breast cancer in women with an abnormal breast cancer gene. This test does not take the place of digital mammography and MRI scanning.

Talk to your doctor, radiologist, and genetic counselor about developing a specialized program for early detection that addresses your breast cancer risk, meets your individual needs, and gives you peace of mind.

Protective surgery: Removing the healthy breasts and ovaries -- called prophylactic surgery ("prophylactic" means "protective") -- are very aggressive, irreversible risk-reduction options that some women with an abnormal BRCA1 or BRCA2 gene choose.

Prophylactic breast surgery may be able to reduce a woman's risk of developing breast cancer by as much as 97%. The surgery removes nearly all of the breast tissue, so there are very few breast cells left behind that could develop into a cancer.

Women with an abnormal BRCA1 or BRCA2 gene may reduce their risk of breast cancer by about 50% by having prophylactic ovary and fallopian tube removal (salpingo-oophorectomy) before menopause. Removing the ovaries lowers the risk of breast cancer because the ovaries are the main source of estrogen in a premenopausal womans body. Removing the ovaries doesnt reduce the risk of breast cancer in postmenopausal women because fat and muscle tissue are the main producers of estrogen in these women. Prophylactic removal of both ovaries and fallopian tubes reduces the risk of ovarian cancer in women at any age, before or after menopause.

Research also has shown that women with an abnormal BRCA1 or BRCA2 gene who have prophylactic ovary removal have better survival if they eventually are diagnosed with breast or ovarian cancer.

The benefit of prophylactic surgeries is usually counted one year at a time. Thats why the younger you are at the time of surgery, the larger the potential benefit, and the older you are, the lower the benefit. Also, as you get older youre more likely to develop other medical conditions that affect how long you live, such as diabetes and heart disease.

Of course, each woman's situation is unique. Talk to your doctor about your personal level of risk and how best to manage it.

It's important to remember that no procedure -- not even removing both healthy breasts and ovaries at a young age -- totally eliminates the risk of cancer. There is still a small risk that cancer can develop in the areas where the breasts used to be. Close follow-up is necessary, even after prophylactic surgery.

Prophylactic surgery decisions require a great deal of thought, patience, and discussion with your doctors, genetic counselor, and family over time -- together with a tremendous amount of courage. Take the time you need to consider these options and make decisions that feel comfortable to you.

For more information, visit the Breastcancer.org Prophylactic Mastectomy and Prophylactic Ovary Removal pages.

Think Pink, Live Green: A Step-by-Step Guide to Reducing Your Risk of Breast Cancer teaches you the biology of breast development and how modern life affects breast cancer risk. Order a free booklet by mail or download the PDF of the booklet to learn 31 risk-reducing steps you can take today.

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Genetics: Breast Cancer Risk Factors