Hereditary cancer information for patients

Introduction: Genetics and cancer

We inherit our genes from our mother and father. Genes are the instructions that build and run our bodies. Each gene is made of a small piece of DNA, which is a string of chemical letters. A change in one or more letters is called a variant or mutation. We can inherit a gene variant from our parents, or we can be the first one in our family to have it.

We can have harmless variants in our DNA. However, some variants can affect our health and development. These are known as pathogenic or disease causing variants. Health conditions that are caused by genetic variants are called genetic or hereditary conditions.

Each gene has a special job to do in the body. Some genes work to protect us from certain types of cancer. If you have a harmful (pathogenic or disease causing) genetic variant in a cancer protection gene, you have an increased genetic risk for cancer.

Further information about inherited cancer can be found here:

Genes and breast cancer

Most breast cancer (95%) is not hereditary.
About 5% of people with breast cancer have a hereditary cause for their cancer due to a genetic variant in a cancer protection gene.
Hereditary breast cancer can be passed through the whānau/family by males and females.

Hereditary breast cancer

Hereditary breast cancer is more likely if you have:

more than one cancer (that is, 2 separate breast cancers or a breast and ovarian cancer)
a strong family history of breast and/or ovarian cancer
triple negative breast cancer
young diagnosis of breast cancer (40 years or younger).

Genes

BRCA1, BRCA2, PALB2

There are several ‘cancer protection’ genes which, if not working, can increase the risk of breast and/or ovarian cancer developing.

The 3 main genes that have been identified are:

Breast Cancer 1 gene (BRCA1)
Breast Cancer 2 gene (BRCA2)
Partner And Localiser of BRCA2 (PALB2).

BRCA1, BRCA2 and PALB2 genes are known more specifically as tumour suppressor genes because their role is to act as the ‘brakes’ on uncontrolled cell growth. Some genetic causes for breast cancer increase the chance of male breast cancer, prostate and pancreatic cancer.

There are other genetic risks that can cause a high risk of breast cancer, but families with these usually also have other specific types of cancer. These conditions are described below under CDH1 and TP53.

Further information can be found here:

CHEK2, ATM, RAD51C and RAD51D

Most variants in these genes are associated with a moderately increased risk of breast cancer. The effect of a pathogenic variant on cancer risk is influenced by family history of breast cancer. Moderate risk genes appear to work in combination with additional personal risk factors, other genetic variants and environmental factors. Assessment of the family history together with genetic results is important to determine the appropriate level of breast screening that is needed for whānau/family.

ATM pathogenic variants are also associated with an increased risk of other cancers including pancreatic and prostate cancer.

RAD51C and RAD51D variants are associated with an increased risk of ovarian cancer. Women are eligible for risk reducing surgical prevention of ovarian cancer at the appropriate age.

TP53

Individuals who have a pathogenic variant in the gene TP53 have the condition called Li-Fraumeni syndrome (LFS). The condition is associated with a high chance of developing several cancers at younger ages. Young breast cancer is often seen for those with this condition as well as other cancer types in children and adults. Management for the increased risk of some of the cancers associated with this condition is available.

CDH1

Individuals who have a variant in the CDH1 gene have the condition Hereditary Diffuse Gastric Cancer. This is an inherited cancer syndrome that is more common in those with NZ Māori ethnicity. Individuals that inherit a change in this gene have an increased chance of developing both stomach and breast cancer. The stomach and breast cancers that happen are of a specific type known as diffuse stomach cancer and lobular breast cancer. The condition is variable with cancer possible in both young adults and older individuals. In some families there is only a family history of breast cancer.

Support group information

Other resources

More information on genetic testing

How a genetic test is done

Your doctor will give you a blood form and then you can go for a blood test at your local lab. If you are having chemotherapy it should be done as part of your pre-chemotherapy bloods.

How long it takes to get genetic test results

Routine testing takes up to 12 weeks, in special cases urgent testing can be done in less than 4 weeks.

How genetic testing impacts insurance

If you are taking out a new insurance policy and you have had a genetic test, you need to disclose the results to the insurance company. This applies to all types of insurance (like life insurance, health insurance or other insurances). Based on the information you disclose, the insurance company may charge more for cover, or exclude coverage for certain conditions. Aotearoa New Zealand does not currently have any protection against genetic discrimination by insurance companies.

What it means for your children if you have a genetic risk for cancer

Each child will have a 50/50 chance of inheriting the genetic risk. They can access genetic testing when they are adults to find out if they have inherited the genetic risk. If your genetic risk is due to the TP53 gene, genetic testing is available from childhood.

How your relatives can get tested if genetic testing shows you have a genetic risk for cancer

We usually recommend starting by testing your close relatives (siblings, mum/dad). Once we know which side of the family the genetic risk has come from, we can then move on to testing wider family members (aunts, uncles, cousins). Your relatives can self-refer to the public Genetic Health Service by contacting their local clinic. If preferred, they could also opt for one of the private options listed on the Human Genetics Society of Australasia website.

New Zealand public genetic services — Human Genetics Society of Australasia (external link)

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