All cancers involve gene mutations, but only some are hereditary.
Cancer occurs when gene mutations cause the normal mechanisms that manage cell growth to fail, resulting in cells reproducing in an uncontrolled way.
Most cancer-causing mutations occur after a person is born, arising randomly as people get older or in response to environmental factors e.g. exposure to hazardous chemicals, radiation, or viruses. Cancers resulting from acquired mutations are called sporadic cancers.
A cancer is considered hereditary if it is linked to an inherited mutation in a type of gene, called a cancer predisposition gene. These mutations are passed down from a parent and so are already present in a person at birth. Though around 90% of cancers are sporadic, hereditary cancers make up approximately 10% of all cancer cases.
Cancer predisposition gene (CPG) mutations do not cause cancer but increase cancer risk.
When functioning normally, CPGs help to avoid uncontrolled cell growth. Mutations in these types of genes can lead to healthy cells becoming cancerous.
Being born with a CPG mutation increases a person’s risk of developing cancer but doesn’t not guarantee that they will get cancer. This is because one gene mutation in a cell is not sufficient to trigger cancer – in general 5 or 6 mutations are required.
Compared to those born without a CPG mutation, people with an inherited mutation need fewer additional acquired mutations for cancer to develop. And so, though they may not definitely get cancer, they are more susceptible – and if they do develop cancer, this will typically happen at a younger age than ones that are not hereditary.
Hereditary cancer risk varies depending on the CPG mutation and other factors.
There are at least 40 CPGs linked with hereditary cancer, some more frequent and well-known than others. This number may well grow in the future with new research and clinical findings.
Different CPG mutations are linked to varying cancer risks, including the types of cancer that may develop and the extent to which the risk is elevated.
An individual’s hereditary cancer risk depends on the specific CPG mutation they have as well as other factors such as their age, lifestyle, and family history of cancer.
Cancer Predisposition Gene (CPG)
CPG mutation frequency in general population
A person with a CPG mutation has a 50% chance of passing it on to their children.
Hereditary cancer is also known as familial cancer because the increased cancer risk is passed on in families, and cancer can develop in multiple relatives across different generations.
As CPG mutations are inherited in a dominant way, there is a 50% chance that a parent (mother OR father) will pass on the mutation – and associated increased cancer risk- with each pregnancy.
Furthermore, each sibling of a person with an inherited CPG mutation has a 50% chance of also inheriting that mutation.
Hereditary cancer risk CAN be managed
Fortunately, people with an identified CPG mutation have various options available to reduce the risk of cancer developing.
These options may include cancer screening and surveillance programmes, prophylactic surgery, medication and lifestyle changes. Together these approaches are designed to either prevent hereditary cancer from developing or catch it earlier when the prognosis is better.
Genetic testing can identify if a person has a CPG mutation, enabling them to access relevant risk management options. Testing is appropriate for people that may have an increased hereditary cancer risk, e.g. if they have a personal or family history of cancer, a relative with a known CPG mutation, or are part of higher-risk ethnic group.