Genetic testing for inherited cancer

A predisposition to certain cancers can be inherited through altered genes. Genetic testing aims to detect a genetic change that may increase a person’s chance of developing a particular cancer. This kind of testing is available to some families who are at high risk of an inherited predisposition to certain cancers.

Genes control the growth, division and life span of every cell in the body. Your genes come in pairs, with one copy inherited from your mother and the other from your father. Some people inherit an altered gene that may predispose them to developing particular cancers.

For example, a woman who inherits a single altered copy of one of the specific breast cancer genes has a higher risk of breast and ovarian cancer than a woman who inherited two normal copies of those genes.

Even so, only around five out of every hundred cases of breast cancer are due to an inherited genetic predisposition. A small number of families have a greater risk of cancers such as breast, ovarian and bowel cancers because they carry a changed gene.

Who may be at higher risk#

A family cancer centre can advise you about your risk of developing cancer, provide genetic counselling and medical advice and, in some situations, arrange genetic testing.

Families who may be at potentially high risk of breast or ovarian cancer include those with three or more relatives who have had breast or ovarian cancer. Families with two or more affected relatives may also be at higher risk when one or more of the following features is present:

• Cancer in both breasts in the same relative
• 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
• Ancestry from a population with a higher carrier rate
• Breast cancer with pathological features that suggest 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 who have had bowel cancer. Families with two or more affected relatives may also be at increased risk when 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 a large number of bowel polyps

For other types of cancer, people are generally considered to be at increased risk if several relatives have the same type of cancer, or if a relative has been found to carry a particular altered gene.

How genetic testing works#

Genetic testing is available to a small number of families at the highest risk of having an inherited predisposition to cancer.

Generally, it is necessary to test a person who has already had cancer first, in order to identify the genetic change causing cancer in the family. If a genetic change is found, it confirms that the cancers in that family are due to an inherited predisposition. Blood relatives who have no signs of cancer can then choose to be tested to find out whether they have inherited the same altered gene and could be at increased risk of developing specific types of cancer.

If a relative has inherited a predisposition to cancer, the family cancer centre will develop a personal program designed to manage their risk.

If a genetic change cannot be found in a person affected by cancer, it remains possible that there is still a genetic predisposition to cancer in the family.

Not all genetic changes can be detected#

The family cancer centre can advise family members about their chance of developing cancer and what they can do to reduce the risk. Genetic testing is arranged through the family cancer centre and is offered only with counselling both before and after the test, so that its limitations as well as its potential benefits can be discussed.

Getting help#

If you believe you may be at risk of familial cancer, see your doctor first. If your doctor thinks there may be cause for concern, an appointment can be made with a family cancer centre. These centres have professional staff including geneticists, genetic counsellors, gastroenterologists, surgeons and oncologists (cancer specialists). The staff can answer your questions, discuss your medical options and explain whether genetic testing is possible.

Key points#

• A predisposition to some cancers can be inherited through altered genes, but only a small share of cancers are due to an inherited predisposition.
• Families with several close relatives affected by the same or related cancers may be at higher risk.
• Testing usually begins with a relative who has had cancer, to identify the genetic change in the family.
• Not all genetic changes can be detected, and testing is offered with counselling before and after.
• See your doctor first if you are concerned about familial cancer.

Where to get help#