The facts about cancer genetic testing

Genetic cancer testing can help identify inherited gene changes that may increase the risk of developing certain types of cancer or for some patients genetic testing can help determine the best treatment for their specific cancer.

Genes control the growth, division and life span of every cell in the body. Your genes come in pairs – one inherited from your biological mother and father.

Some people inherit altered genes that may increase the risk of developing cancers. For example, a woman who has inherited a single altered copy of one of the specific breast cancer genes (known as BRCA1 and BRCA2) has a higher risk of breast and ovarian cancer than a woman who inherited two normal copies of both genes.

A small number of families have a greater risk of certain cancers such as breast, ovarian and bowel cancers because they carry a changed gene.

Families who may be at potentially high risk of breast or ovarian cancer include those with three or more relatives with breast or ovarian cancer.

Families with two or more relatives who have breast or ovarian cancer are also considered to be at potentially high risk, if the affected relatives fall into any of the following categories:

• cancer in both breasts
• onset of breast cancer before the age of 40
• ovarian cancer at any age
• breast and ovarian cancer in the same relative
• breast cancer in a male relative breast cancer has pathological features that suggest the presence of an inherited predisposition

Families who may be at potentially high risk of bowel cancer include those with three or more relatives on the same side of the family with bowel cancer.

Families with two or more relatives with bowel cancer are also considered to have an increased risk if there is:

• more than one bowel cancer in the same relative
• onset of bowel cancer before the age of 50
• a relative with endometrial or ovarian cancer
• a relative with bowel cancer and with a large number of bowel polyps

For other types of cancers, people are at increased risk if they have:

• several relatives who have the same type of cancer
• a relative who has been found to carry a particular altered gene

Genetic testing is available to families at high risk. Generally, it is necessary to test a family member who has had cancer first to identify the genetic change causing cancer in the family. If a genetic change is found, blood relatives who have no signs of cancer can then choose to have testing to find out if they have inherited the altered gene which could increase their risk of developing cancer.

Genetic counselling gives you information that you and your family can use to make decisions about whether to get genetic testing.

Before and after genetic testing, a genetic counsellor can help you understand:

• your risk of getting certain types of cancer based on your family’s medical history
• what you can do about this risk
• which genetic tests can give you more information about your risk level
• what your test results might mean

Your counsellor will explain the testing process and tell you more about what the tests can and cannot do. Together, you will also discuss how the test results may affect your emotions, mental health, and family.