The Genetics of Breast Cancer

After we talked about The Genetics of Cancer, it is time we will provide the posting about The Genetics of Breast Cancer, Genes carry small individual collections of information in each cell of the human body. Each gene consists of a unique DNA sequence. Researchers in the Human Genome Project is estimated that nearly 30,000 different genes in each cell. The genes are packaged into chromosomes. There are 23 pairs of chromosomes in each cell. One chromosome of each pair inherited from the father of the person and the other from the mother of the person.

Genes control how a cell, including how fast it grows, how often they divide, and how long you live. To control these functions, genes produce proteins that lead to specific tasks and act as messengers in the cell. Therefore, it is important that each gene is the proper instructions or "code" for the production of its protein-protein can be so the proper functioning of the cell has to fulfill

What role do genes play in breast cancer?

Cancer begins when one or more genes in a cell are mutated (changed), creating an abnormal protein or no protein at all. The information provided by an abnormal protein is different from that of a normal protein, which can cause cells to multiply uncontrollably and become cancerous.
A person may either be born with a genetic mutation in all of their cells (germline mutation) or acquire a genetic mutation in a single cell during his or her lifetime. An acquired mutation is passed on to all cells that develop from that single cell (called a somatic mutation). Somatic mutations can sometimes be caused by environmental factors, such as cigarette smoke. Most breast cancers (about 90% to 95%) are considered sporadic, meaning that the damage to the genes occurs by chance after a person is born. Inherited breast cancers are less common (5% to 10%) and occur when gene mutations are passed within a family, from one generation to the next. Genetic mutations in certain types of genes are more likely to cause cancer. The most common gene mutations that can increase breast cancer risk occur in tumor suppressor genes. A tumor suppressor gene makes proteins that prevent tumor formation by limiting cell growth. Mutations in a tumor suppressor gene cause a loss of the ability to restrict tumor growth and, as a result, cancer can develop.

What are the chances a mutated gene is inherited?

Every cell usually has two copies of each gene: one inherited from the mother and one inherited from the father. Breast cancer usually follows an autosomal dominant inheritance pattern, in which a mutation needs to happen in only one copy of the gene for the person to have an increased risk of getting the disease. This means that a parent with a gene mutation may pass on a copy of the normal gene or a copy of the gene with a mutation. Therefore, a child who has a parent with a mutation has a 50% chance of inheriting that mutation. A brother, sister, or parent of a person who has a gene mutation also has a 50% chance of having the same mutation.

What is a woman's average risk for breast cancer?

A woman with an average risk of breast cancer has about a 12% chance of developing breast cancer.

How common is breast cancer?

Breast cancer is the most common cancer among women, excluding cancers of the skin, and the second most common cause of death from cancer among women. In 2009, an estimated 192,370 women in the United States will be diagnosed with invasive breast cancer, and 62,280 women will be diagnosed with in situ breast cancer. An estimated 1,910 men in the United States will be diagnosed with breast cancer. It is estimated that 40,610 deaths (40,170 women, 440 men) from this disease will occur this year.

How can a woman know if she has inherited a genetic mutation that increases her risk of breast cancer?

Only genetic testing can determine whether a person has a genetic mutation. Most experts strongly recommend that people considering genetic testing first consult a genetic counselor. Genetic counselors are trained to explain the risks and benefits of genetic testing.

For more information, read Genetic Testing and What to Expect When Meeting With a Genetic Counselor.

How does a woman know if breast cancer runs in the family?

Breast cancer may run in the family if first-degree relatives (mothers, sisters, children) or many close relatives (first-degree relatives, grandmothers, aunts, nieces, granddaughters, cousins) have been diagnosed with breast cancer, especially before age 50.

What is a woman's risk if breast cancer runs in the family?

If a woman's first-degree relative developed breast cancer, the woman’s risk is double the average woman's risk. If two first-degree relatives developed breast cancer, the woman’s risk is 5 times the average risk. It is uncertain how much a woman's risk of breast cancer is increased when a man in the family has breast cancer.

Which inherited genetic mutations raise the risk of breast cancer?

There are several genes linked to an increased risk of breast cancer. Some of the most common hereditary cancer syndromes associated with breast cancer risk are described below.

Hereditary breast and ovarian cancer (HBOC) syndrome. The two genes are associated with HBOC, BRCA1 and BRCA2 (BRCA stands for BReast CAncer), are tumor suppressor genes. Women who inherit a BRCA mutation have a 50% to 85% chance of developing breast cancer and a 15% to 40% chance of developing ovarian cancer. Men with BRCA1 and BRCA2 mutations may have an increased risk of breast and prostate cancers. Both women and men with BRCA2 mutations may be at increased risk of breast cancer or other types of cancer. Approximately one in 40 women with Ashkenazi Jewish heritage carry a mutation in BRCA1 or BRCA2 genes that increases their risk of breast cancer to between 50% and 85%. Their risk of ovarian cancer is also increased to about 40%. About 80% of hereditary (inherited) breast cancer is caused by mutations in BRCA1 or BRCA2.

For more information, read the Cancer.Net Cancer.Net Guide to Hereditary Breast and Ovarian Cancer.

Ataxia telangiectasia (A-T). Ataxia-telangiectasia (A-T) is a rare recessive disorder characterized by progressive neurological problems that lead to difficulty walking. Signs of A-T develop in childhood. Children may begin staggering and appear unsteady shortly after learning to walk. Most people with A-T will eventually need to use a wheelchair. Slurred speech and difficulty with writing and other tasks develop over time. Red marks that are caused by dilated capillaries (tiny blood vessels), called telangiectases, often appear on the skin and eyes. People with A-T also have a weakened immune system and are prone to infections.

There is about a 40% risk of cancer for people with A-T. The most common cancers associated with A-T are leukemia and lymphoma. As the lifespan of individuals with A-T increases, other types of cancer, including melanoma, sarcoma, and breast, ovarian, and stomach cancers, are being reported in adults. However, it is too early to determine if there is truly an increased risk for these cancers that is caused by A-T, or whether these are sporadic cancers developing in adults who also happen to have A-T.

A-T is inherited as an autosomal recessive condition. In autosomal recessive inheritance, a person needs to have two copies of a gene mutation in order to have the disease. This means that each parent must have one mutated gene and one normal gene. If both parents carry a gene mutation for A-T, each of their children will have a 25% chance of inheriting both gene mutations and having A-T. The gene associated with AT is called ATM. For people who have one altered copy of the gene, there may be a somewhat increased risk of melanoma and breast, ovarian, and stomach cancers. Genetic testing for the ATM gene is available.

For more information, read the Cancer.Net Guide to Ataxia-Telangiectasia.

Li-Fraumeni syndrome (LFS). People with LFS have up to a 50% chance of developing cancer by age 40 and a 90% chance of developing cancer by age 60. Some of the cancers most commonly associated with LFS are osteosarcoma (a type of bone cancer), soft tissue sarcoma, leukemia, breast cancer, brain cancer, and adrenal cortical tumors. An adrenal cortical tumor begins in the adrenal cortex, which is the outer layer of the adrenal glands. The adrenal glands are located on top of each kidney and are a part of the body’s endocrine (hormonal) system.

LFS is a rare condition. The gene associated with LFS, called p53, is a tumor suppressor gene. Testing for p53 gene mutations is available for families who may have LFS. Another gene, CHEK2, may cause LFS for some families. Testing for mutations in the CHEK2 gene is only available as part of a research study.

For more information, read the Cancer.Net Guide to Li-Fraumeni syndrome.

Cowden syndrome (CS). Women with CS have a 25% to 50% risk of developing breast cancer and a 65% risk of developing noncancerous breast changes. CS is a rare genetic condition caused by a mutation on the PTEN gene. People with CS also have a high risk of both noncancerous and cancerous tumors of the thyroid and endometrium (lining of the uterus). Also, people with CS often have small growths on the face or in the mouth and a larger than average head size. Genetic testing for the PTEN gene is available.

For more information, read the Cancer.Net Guide to Cowden Syndrome.

Peutz-Jeghers syndrome (PJS). Women with PJS have approximately a 50% risk of developing breast cancer. Women with PJS also have about a 20% risk of developing ovarian cancer. People with PJS often have multiple hamartomatous polyps, which are normal-appearing growths in the digestive tract that become a noncancerous tumor. These polyps cause an increased risk of colorectal cancer. People with PJS also have increased pigmentation (dark spots on the skin) on the face and hands. The increased pigmentation often appears in childhood and fades over time. Families with PJS also have an increased risk of uterine and lung cancers. The gene associated with PJS is called STK11. The STK11 is a tumor suppressor gene, and genetic testing for the STK11 gene is available.

For more information, read the Cancer.Net Guide to Peutz-Jeghers Syndrome.

Other genes. Other genes may cause hereditary breast cancer. However, more research is needed to understand how gene mutations can increase breast cancer risk and to find other genes that may increase a person’s risk of breast cancer.

What is a person's risk level?

In addition to family history, other environmental and lifestyle factors may increase the risk of breast cancer. Discussing family history and personal risk factors with a doctor can help a person better understand his or her risk. People with a higher than average risk may benefit from genetic counseling and early detection strategies.

A risk factor is anything that increases a person's risk of developing cancer. Having a particular genetic mutation linked to breast cancer cannot predict that a person will develop cancer. Controllable risk factors, such as eating a balanced diet, maintaining a healthy weight, exercising, limiting alcoholic beverages, and avoiding tobacco products also play a role. Most people who develop breast cancer have few known risk factors. Research to better understand the link between genetic mutations and breast cancer is ongoing. Talk with a doctor for more information about risk factors, prevention, and screening for breast cancer.
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