Cancer and genes

In normal adult tissues the rate at which new cells are made (cell growth) and old cells die is in balance. Genes inside each cell maintain this balance by controlling how the cell behaves.

There are many different types of genes that control cell behaviour. Cancer is the result of changes (mutations) in genes that control cell growth and death. Cells with such mutations may begin to grow in an uncontrolled way, forming tumours. Usually several gene mutations must happen in a group of cells before cancer develops. This can take many years, and is why cancer is more common in older people.

Oncogenes and tumour suppressor genes Back to top

Changes in two types of genes are particularly important for cancer development. These genes are called oncogenes and tumour suppressor genes.

Oncogenes encourage the cell to grow and multiply. A change (mutation) in this type of gene can lead to a cell growing and multiplying out of control.

Tumour suppressor genes help to protect against cancer by controlling cell growth and repairing damage to our genetic code (DNA).

Tumour suppressor genes that control cell growth tell the cell when to stop growing (multiplying). If a cell has a mutation in a tumour suppressor gene the ‘brakes’ on its growth may be lost so it can multiply out of control. Some tumour suppressor genes help to protect against cancer by repairing damage to DNA. They are called DNA repair genes or caretaker genes. When there is a fault (mutation) in a DNA repair gene, any new damage or mutations in the cell won’t be repaired. So, cancer is more likely to develop.

Inherited and acquired mutations Back to top

There are two types of mutations:

• Mutations that someone is born with and that are passed down from generation to generation (inherited mutations).
• Mutations that happen in a part of someone’s body during their lifetime (eg their lung or bowel) and aren’t passed on to the next generation (acquired mutations).

Inherited mutations (also known as germline mutations)

These are gene changes inherited from your mother or father. All the cells of your body develop from one cell. So, if you inherit a gene mutation, all the cells in your body contain the genetic change. Because the mutation is also in reproductive cells (sperm cells in men and egg cells in women), it can be passed on from generation to generation.

Inherited gene mutations that make a cancer more likely to develop are sometimes called cancer susceptibility genes. More than one mutation is needed for a cancer to develop. So inheriting a cancer susceptibility gene doesn’t mean a person has cancer but that they are at increased risk of developing certain types of cancer. Cancers that run in families because of an inherited gene mutation which causes a susceptibility to that type of cancer are sometimes referred to as inherited cancers|.

Acquired mutations (also known as somatic mutations)

These happen during a person’s lifetime. An acquired mutation happens in one cell in a person’s body and only affects the cell it begins in, and any new cells made from the abnormal cell. Acquired mutations can’t be passed on to your children.

Acquired mutations can happen by chance when a cell is multiplying or because a gene is damaged. Some substances, called carcinogens, are known to increase the chance of damage to genes. Examples of known carcinogens include radiation and chemicals in cigarette smoke.

Cancers caused by a build up of acquired mutations during a person’s lifetime are called sporadic cancers. Most cancers are sporadic cancers.