Human Genetic Variation
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Breast Cancer

a mass of tumor cells amongst normal cellsCauses

A person's cells contain a variety of genes that normally work together to control cell division so that more cells are produced only when the body needs them. The transformation of a cell from normal to cancerous requires that the cell experience several separate changes (mutations) in the genes that control division. When such changes occur in breast or other tissue, cells keep dividing even when new cells are not needed, and a tumor may form.


Cancer is a group of more than 100 diseases that occur when cells become abnormal and divide without control or order. This abnormal division may produce a tumor that can be benign (not cancerous) or malignant (cancerous). Malignant tumors can invade, damage, and destroy nearby tissues and spread to other parts of the body.

There are several types of breast cancer. The most common begins in the lining of the milk ducts of the breast. Another type begins in the lobules where milk is produced. If a malignant tumor invades nearby tissues (for example, lymph nodes in the area), it is known as invasive cancer.


The earliest sign of breast cancer is usually an abnormality that shows up on a mammogram (a special X-ray of the breast) before it can be felt by the woman or a health care provider. When breast cancer has developed to the point where physical signs and symptoms exist, these symptoms may include a lump, thickening, swelling, distortion, or tenderness in the breast, or skin irritation or dimpling.

The value of mammography is that it can help health care workers identify breast abnormalities that may be cancer at an early stage before physical symptoms develop. Many studies have shown that early detection increases survival and expands treatment options.

Most breast lumps are not cancerous, but only a physician can determine this. When a woman has a suspicious lump, or when a suspicious area is detected on a mammogram, further tests are typically done in order to make a definite diagnosis.


Breast cancer is the most frequently diagnosed non-skin cancer and the second most common cause of death for American women. Approximately 178,000 new cases of invasive breast cancer were expected to be diagnosed in the United States in 1998. This number translates to an incidence rate of about 110 cases per 100,000 women. About 1,600 new cases of invasive breast cancer were expected to be diagnosed in men.

Managing Risk

What are the options available to a person who is found to have a mutation in a BRCA1 or BRCA2 gene? The National Cancer Institute (NCI) lists the following options:

Related Genes

Approximately 5 to 10 percent of women with breast cancer have a hereditary form of the disease. These women have inherited an altered form of one of the several genes involved in the control of cell division. For example, scientists believe that inherited mutations in the BRCA1 and BRCA2 genes are involved in 30 to 70 percent of all inherited cases of breast cancer. Although inheriting one of these mutated genes does not guarantee that a woman will develop breast cancer, it does increase her risk.

Scientists now have tests that can detect mutated BRCA1 and BRCA2 genes with 90 to 95 percent accuracy. Current technology has limited sensitivity and will miss some mutations. However, when someone with a cancer diagnosis and a family history of the disease has been tested and found to have a mutated BRCA1 or BRCA2 gene, the family is aid to have a "known mutation." Others in the family can now be tested to see if they have that mutation. Once a mutation is identified within a family, the testing of relatives at risk is close to 100 percent accurate.

A positive test indicates that a person has inherited a known BRCA1 or BRCA2 mutation and has an increased risk of developing breast and ovarian cancer. In addition, evidence from several studies has shown that a man with a mutated BRCA1 or BRCA2 has a small increased risk of developing prostate cancer. However, a positive result only provides risk information and does not indicate whether or when cancer might develop. A positive result also does not provide any information about how a woman will respond to medical treatment should cancer be diagnosed. It is important to note that many, but not all, women who inherit a mutated BRCA1 or BRCA2 gene will develop breast or ovarian cancer.

Both men and women who inherit a mutated gene, whether or not they develop cancer themselves, can pass the mutation on to their sons and daughters.

A negative BRCA1 or BRCA2 test will be interpreted differently, depending on whether a family mutation is known. If a known mutation is not found in certain family members, those individuals do not have an increased risk for breast cancer based on family history and cannot pass the family risk on to their children.

However, in cases where no BRCA1 or BRCA2 mutation has previously been identified in a family, a negative test is not very informative. It is not possible to tell whether the person actually has a mutation but the test missed it (false negative) or whether the result is a true negative. Furthermore, a woman may have a mutation in a gene other than BRCA1 or BRCA2 that increases her cancer risk but is not detectable by this test.

Risk Factors

Overall, American women have a 1 in 8 chance of developing breast cancer sometime in their lifetimes.

No one knows why some women develop breast cancer and others do not. Over the years, however, researchers have identified certain characteristics, called "risk factors," that influence a woman's chance of developing the disease. For example, the risk of developing breast cancer increases with age. The risk is also higher in women who have a personal history of breast cancer or a family history of breast cancer. Other factors that can increase a woman's risk of developing breast cancer include early onset of menstruation, late menopause, recent use of oral contraceptives, and never having children or having the first live birth at a late age.

Most women will have one or more risk factors for breast cancer. However, many women who develop breast cancer have no known risk factors other than growing older, and many women with known risk factors do not get breast cancer.


The five-year survival rate for localized breast cancer (cancer that has not spread) has increased from 72 percent in the late 1940s to more than 95 percent today.

If the cancer has spread regionally, however, the five-year survival rate is 76 percent. If it has spread to distant sites, the rate is 21 percent.


Depending on the medical situation and the patient's preference, treatment may involve lumpectomy (removal of the tumor) and removal of the lymph nodes under the arm; mastectomy (removal of the breast) and removal of the lymph nodes under the arm; radiation therapy; chemotherapy; or hormone therapy. Sometimes two or more treatment approaches are used in combination.

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