Breast Cancer and Understanding Genetic Testing

By Harwood, Kerry V RN, MSN

Cancer is a disease of the genes. Most cancers develop as a result of genetic damage or a mutation that happens sometime during a person's lifetime. These are called "sporadic" cancers. These types of mutations only affect the cells that grow from the original mutated cell.

The risk of developing cancer is higher in people who are born with certain genetic defects that are passed on from their parents and found in every cell in their body. These defects occur in areas of the DNA that affect cell division, cell death, and the repair of damaged DNA. Cancers that result from DNA damage that is passed on are called "hereditary" cancers. They account for about 5 to 10 percent of all breast cancer cases. The likelihood of breast cancer being hereditary is influenced by your age at the time of diagnosis. The younger you are, the more likely the cancer is hereditary.

The National Cancer Institute describes genes as "nature's blueprints for every living thing." Genes determine your body's potential for function and growth. Environmental factors influence the outcome. For example, a woman might have the genetic potential to be six feet tall. However, if she has poor nutrition as a child, she may not reach that potential. Similarly, a woman may have a genetic risk of developing breast cancer. Whether she develops it or not may be influenced by other exposures she has during her lifetime.

Genes come in pairs. One set is passed down (inherited) from your mother and the other set from your father. Genetic risks and potential can come from either parent.

A number of genetic defects can result in an increased risk for breast cancer. All these defects occur in areas of the genes that influence cancer progression. The most common defects are found on genes named BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2). A woman who has inherited a harmful mutation in BRCA1 or BRCA2 is at higher risk of developing breast cancer and some other types of cancer than a woman who does not have such a mutation. The discoveries of these breast cancer genes in the early 1990s greatly helped our understanding of the genetic basis of inherited breast cancer and ovarian cancer. However, these are large and complex genes. Scientists continue to work to understand the significance of different alterations in these genes.

The National Human Genome Research Institute developed a test that can easily distinguish between hereditary and sporadic forms of breast cancer. This test is called gene-expression profiling. It uses a DNA chip, called a microarray, to assess how active 6,000 different genes are at the same time within a breast tumor. The researchers have proved that they can look at the patterns and determine if the cancer is hereditary or sporadic (nonhereditary).

Deciding on Genetic Testing for Breast Cancer

Genetic testing is considered only for women with a certain family history. You might fall into this high-risk group if any of the following statements are true for you.

  • You have two or more close relatives with breast cancer.

  • You have relatives who developed breast cancer before age 50.

  • You have breast cancer in more than one generation in your family.

  • You have several family members who have had ovarian cancer.

  • You are of Ashkenazi (eastern and central European) Jewish ancestry.

If you are considering genetic testing for cancer risks, you face many complex issues. If you test positive, you will face difficult decisions about treatments to prevent breast cancer. You may have increased anxiety about developing breast cancer. You may have concerns about losing your health insurance coverage. If you test negative, you may also face difficult challenges, such as survivor guilt, if other family members have tested positive.

However, if you are anxious or considering preventive surgery based on your family history, having the results may be very helpful. Because of these issues, you should seek genetic counseling before, during, and after any genetic testing.

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