Cancer develops when a single cell in the body multiplies uncontrollably, producing many copies of itself. Cells become cancerous when there are changes (variants) in the genes that make up the genetic code. Every cell has a copy of the genetic code, and it tells them when to divide and multiply. Variants in the genetic code that cause a health condition such as cancer are called pathogenic variants.
Changes in the genetic code that alter the way cells divide and multiply may occur randomly during a person’s lifetime. The changes may also be caused by carcinogens in the environment, such as chemicals, UV light, or viruses, which can damage the genetic code.
Sometimes these changes do not occur during a person’s lifetime and were inherited (passed down) from a parent. Having a genetic change does not mean cancer will develop. It simply means it is more likely that cancer will develop compared with the general population.
Changes in certain genes are most often associated with the development of cancer. These genes are known as cancer predisposition genes. This means that if a person has a change in one of these genes, they are more likely to develop cancer than someone who does not have the genetic change. The likelihood varies depending on the gene and the particular change in the gene.
There are two main types of cancer predisposition genes:
- Tumour suppressor genes. These play a key role in preventing cells from growing and multiplying. These are also known as cancer protection genes.
- Oncogenes. Pathogenic variants in these genes can increase the risk of the cell growing and multiply uncontrollably.
This article by the American Cancer Society gives more information about these the different types of genetic changes in cancer.
Genetic testing for people with cancer that may be inherited
Most people do not need to be tested to find out if their cancer developed due to an inherited genetic change. This is because most cancers are not caused by inherited genetic changes.
In a very small number of families, certain cancers develop because of a genetic change that was passed down from parent to child. The most common cancers that may be caused by changes in cancer predisposition genes are breast cancer, prostate cancer, bowel cancer, ovarian cancer, melanoma, and kidney cancer.
Genetic testing when there is a strong family history of cancer
People who have a strong family history of cancer may benefit from genetic testing. Examples of a family history include:
- Multiple close relatives with cancer across multiple generations
- Relatives with a cancer that develops at a young age (before 50 years)
- Relatives with more than one type of cancer or rare cancer
- Relatives with similar types of cancer.
Genetic testing can detect changes in specific genes that increase the risk of developing certain cancers. Knowing if a cancer predisposition is inherited can have important benefits for the individual and their family.
If a person is known to be at increased risk of developing a certain type of cancer, preventive strategies can be put into place, such as lifestyle changes, regular screening, or surgery. These strategies may reduce the risk that the cancer will develop or allow the cancer to be detected and treated early. Identifying other family members with the same genetic change means preventive strategies can also be put into place for these individuals.
Cancer genetic testing
At First Light Genetics, we provide comprehensive assessment, testing and counselling to people with cancer that may be inherited, and those with a strong family history of cancer.
We first look closely at the individual and family’s medical and cancer history and draw a family tree. If this suggests there may be a genetic basis for the cancer, we will talk about the different types of genetic testing, including possible outcomes. We will then arrange suitable genetic testing.
If a genetic cause is found, we will explain the result and its possible impact on the individual and related family members. We can also counsel and arrange genetic testing for other family members.
Breast cancer
Most cases of breast cancer are not due to inherited changes in cancer predisposition genes. However, about 5-10% of people with breast cancer have an inherited predisposition to developing this cancer.
The most common cancer predisposition genes are BRCA1, BRCA2 and PALB2. BRCA1, BRCA2 and PALB2 are tumour suppressor genes.
In some families there is a strong family history of breast cancer but no identified genetic changes in BRCA1, BRCA2 or PALB2. This suggests that other genes may increase susceptibility to developing breast cancer.
This fact sheet gives more information about inherited predisposition to breast cancer.
Prostate cancer
Prostate cancer is one of the most common cancers in men, and usually develops after the age of 55 years. Around 5-10% of cases of prostate cancer are thought to be due to an inherited predisposition.
No single cancer predisposition gene has been identified for prostate cancer. However, people with changes in the tumour suppressor genes BRCA1 and BRCA2 have been found to have an increased likelihood of developing prostate cancer compared with the general population.
This fact sheet explains more about inherited predisposition to prostate cancer.
Bowel cancer
Like breast and prostate cancer, most cases of bowel cancer are due to chance, not to inherited predisposition. However, some inherited conditions increase the likelihood that cancer will develop. These are due to inherited changes in tumour suppressor genes. These conditions include:
- Familial adenomatous polyposis
- Lynch Syndrome
- MUTYH-Associated Polyposis.
This fact sheet gives more information about these conditions.
Ovarian cancer
Around 20% of women who develop ovarian cancer have an inherited predisposition. This may be related to changes in several different genes, including BRCA1 and BRCA2. Changes in other genes also appear to increase the risk of developing ovarian cancer.
This website gives more information about inherited predisposition to ovarian cancer.
Melanoma
In around 2% of people with melanoma, an inherited change in a cancer predisposition gene is thought to have caused the cancer. An inherited predisposition may be suspected if a family has:
- Two close relatives with melanoma
- Three or more cases of melanoma in a family.
A number of different tumour suppressor genes may be responsible for melanoma. The most common gene is known as CDKN2A. People with an inherited change in this gene have a 1 in 2 chance of developing melanoma by the time they are 80 years old.
This fact sheet gives more information about melanoma and inherited susceptibility.
Kidney cancer
Up to 10% of kidney cancers are thought to be due to inherited changes in cancer predisposition genes. There are four inherited conditions associated with kidney cancer:
- Von Hippel-Lindau disease (VHL)
- Hereditary leiomyomatosis and renal cell cancer (HLRCC)
- Birt Hogg-Dubé syndrome (BHD)
- Hereditary papillary renal cancer (HPRC)
This website gives more information about kidney cancer and these conditions.
Frequently asked questions
Cancer genetic testing may be advisable if you have a family history of cancer, including:
- Multiple close relatives with cancer across multiple generations
- Relatives with a cancer that develops at a young age (before 50 years)
- Relatives with more than one type of cancer or rare cancer
- Relatives with similar types of cancer.
Genetic tests for cancer are usually done on a sample of blood, saliva or cheek swab (gentle scrape of the inside of your mouth). Sometimes a sample of a different tissue type may be taken (such as skin or hair follicles).
Some Australians can access genetic testing through Medicare if they meet certain criteria such as a previous diagnosis of cancer and/or a family history of inherited cancer.
If a pathogenic variant in a cancer predisposition gene has been found in a relative, we will provide counselling and then arrange predictive genetic testing. This type of testing is used to identify genetic changes in a person who is not showing any signs of cancer.
This type of genetic test is known as a targeted test. This means the result will tell us whether or not you have a change in the same cancer predisposition gene as your relative.
If a pathogenic variant in a cancer predisposition gene is found, we can then advise the likelihood of developing certain cancers. We can also refer you for preventive medical treatment. This may involve regular screening to identify cancer at an early stage, or taking steps to prevent cancer before it develops, for example having a mastectomy (breast removal).
It means you have a change in a gene that increases your risk of developing cancer. A positive result does not mean you will definitely develop cancer, just that your risk is increased compared with people who do not have a genetic change.
Having this knowledge will mean preventive strategies can be put into place to detect cancers at early stage or to prevent cancer from developing, for example, having a mastectomy (breast removal) to prevent breast cancer or an oophorectomy (removal of ovaries) to prevent ovarian cancer.
No. Predictive testing is targeted and can only detect a specific genetic change that is known to be in your family. Having a negative predictive test might put you at the same risk of developing cancer as the general population.
