All cancers are caused by a permanent change in, or damage to, one or more genes. Genes are present in every cell in your body and guide how each cell develops, behaves and functions. A change in a gene is called a gene mutation. A mutation in a gene changes the instructions it gives to the body and stops it from working properly, which can upset normal development or cause a medical condition. Gene mutations have varying effects on health. Their effects depend on where they occur and whether they change the function of essential proteins.
Some genes help control cell growth and play a role in cancer cell development. For example, a change can occur in a gene that promotes cell growth or in a gene that slows cell growth and normally protects against cancer (tumour suppressor gene). Mutations in these genes can allow cells to grow out of control and contribute to cancer developing.
Each cell has the ability to spot changes in DNA and fix them before they are passed on to new cells. Sometimes a cell’s ability to make these repairs fails and the change is passed on to new cells. The cells that have damaged DNA are more likely to become cancerous. Several mutations usually have to occur before a normal cell changes into a cancerous one.
Scientists have learned a great deal about how changes in our genes can affect our health and increase the risk of cancer.
Sporadic (acquired or non-inherited) cancers
Some cancers are due to the genes we are born with. Other cancers are due to gene changes that happen during our lifetime. Sporadic (acquired) cancers are due to mutations that happen as we get older or because of age, chance or something we are exposed to (carcinogen). Sometimes these mutations are errors that occur during cell division. They can also be caused by something that damages the cell’s DNA. Mutations can affect the structure of the gene and stop it from working properly. The majority of cancers are sporadic (caused by acquired gene mutations).
Inherited (hereditary) cancers
Only a few cancers (about 5%–10%) are caused by inheriting a certain gene mutation. These are commonly referred to as inherited (hereditary) cancers, but this term is not very accurate. Cancer cannot be inherited. Instead, a particular gene mutation is inherited. This mutation makes a person more susceptible or predisposed to developing cancer. Although inheriting the mutation increases the risk of developing cancer, it does not always mean that a person will definitely get cancer during their lifetime. Often with hereditary cancers, the person who develops cancer tends to develop it at an earlier age than the rest of the population.
Many types of cancer have been linked to heredity. Examples of cancers sometimes caused by an inherited gene include breast and colon cancer in adults and retinoblastoma in children.