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Lynch Syndrome - What it is

Lynch syndrome is a hereditary cancer syndrome.

What is Lynch syndrome?

Lynch syndrome is an adult-onset hereditary condition that runs in families. It is associated with an increased risk of developing colorectal cancer as well as other cancers.

Approximately 2-5% of all colorectal cancer cases is associated with a hereditary cancer syndrome.

How common is Lynch syndrome?

Estimates suggest that one in 300 people may carry a faulty copy of a DNA mismatch repair (MMR) gene associated with Lynch syndrome.

Approximately, up to 5% of colorectal cancer and 3% of endometrial (uterine) cancer cases are caused by Lynch syndrome.

Causes of colorectal cancer
Sporadic Largely caused by chance events, driven by age and environmental factors	~75%
Familial / polygenic A combination of genes and environmental factors resulting in an elevated cancer risk	Up to 30%
Hereditary There are different hereditary cancer syndromes associated with an increased risk of colorectal cancer, of which Lynch syndrome is the most common	2-5%

Causes of colorectal cancer

Sporadic

Largely caused by chance events, driven by age and environmental factors

~75%

Familial / polygenic

A combination of genes and environmental factors resulting in an elevated cancer risk

Up to 30%

Hereditary

There are different hereditary cancer syndromes associated with an increased risk of colorectal cancer, of which Lynch syndrome is the most common

2-5%

What is hereditary cancer?

Hereditary cancer makes up about 5-10% of all cases of cancer. Some genes function to protect us from cancer. When they are not working well, it causes hereditary cancer. We refer to genes that are not working well as faulty genes.

Individuals who carry a faulty cancer gene(s) have a higher chance of developing certain cancers over their lifetime compared to the general population. The types of cancers that they may be at increased risk of will depend on the gene(s) involved.

If you have a faulty cancer gene, you may be at increased risk of developing certain cancers. As genes are shared among family, other family members may have inherited the faulty gene and may be at increased risk of cancer too.

Hereditary cancer accounts for up to 10% of all cases of cancer.

What is genetic testing?

Genetic testing is offered to individuals where a hereditary cause of their personal and/or family history of cancer is suspected.

Genes contain the instructions that our body reads to carry out different functions. Genetic testing involves analysing your genes to understand if there are faults (i.e., mutations) that may increase the risk of diseases like cancer.

How is genetic testing done?

Genetic testing is typically a one-time blood test.
If a blood sample cannot be taken, other sample sources (e.g., skin or saliva) may be used.

What are the possible results of genetic testing?

There are 3 types of results you may receive:

Positive	Uncertain - Variant of Uncertain Significance (VUS)	Negative
Faulty gene(s) identified	Uncertain gene change(s) identified, unclear if these change(s) increase risk for tumours and cancers	No faulty gene(s) identified
Increased risk of developing certain tumours and cancers (depends on faulty gene(s) involved)	May be clarified by testing other family members	Tumour and cancer risk is similar to that of general population
Your family (parents, siblings, children and extended relatives) may have inherited the faulty gene(s) and should consider genetic testing to clarify this	May be reclassified over time as ‘positive’ or ‘negative’ when more information is known	Test limitations will be explained in the context of your personal and family history of tumours and cancers