Many cancers begin 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 and there is no risk of passing on the gene to a person's children. Inherited breast cancers are less common (5% to 10%) and occur when gene mutations are passed within a family from one generat ...more

Some junk genes have been identified for breast cancer..

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 and there is no risk of passing on the gene to a person's children. 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.

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Some women have a very high risk of breast cancer because they inherited changes in certain genes. The genes most commonly involved in breast cancer are known as BRCA1 and BRCA2. Women with mutations in these genes have up to an 80 percent chance of getting breast cancer at some point in life. Other genes may be linked to breast cancer risk as well.