Cancer and genes

Some genes control when new cells are made and old cells die, and repair damaged DNA. Changes (mutations) in these genes can increase the risk of cancer developing.

There are two types of mutations, called acquired mutations and inherited mutations. Acquired mutations happen during a person’s lifetime, and can’t be passed on to their children. They can happen by chance when a cell is multiplying or because a gene is damaged. Some substances, such as cigarette smoke, can increase the chance of gene mutations.

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

Inherited mutations are gene mutations that you are born with. They can be passed on to your children. Inherited gene mutations that make a cancer more likely to develop are called cancer susceptibility genes. If you inherit these genes, it doesn’t mean you’ll definitely get cancer, but you may be at an increased risk of developing it.

There are inherited cancer genes for some cancers, including breast, bowel, ovarian and womb.

Other cancers, including prostate, pancreatic and testicular, happen in some families more than usual. But specific inherited cancer genes haven’t been found for these cancers yet.

Genes and how they work

Our body is made up of tiny building blocks, called cells. Cancer develops when some cells are damaged and our body can’t repair them. The damaged cells keep growing out of the body’s control. These are cancer cells.

There are genes in every cell. All cancers are caused by changes (mutations) in genes. Genes contain the information a cell needs to work properly. This information is in a code called DNA (deoxyribonucleic acid).

Our body needs to make new cells to replace old or damaged ones. Genes control this process. They also tell cells how to repair damage. If a cell can’t be repaired, or is not needed, genes inside the cell tell it to die.

The genes that control cell growth, repair and death are called oncogenes and tumour suppressor genes. Mutations in these types of gene can increase the chance of cancer developing.

Oncogenes

These genes encourage cells to grow and multiply. A mutation in an oncogene can lead to a cell growing and multiplying out of control.

Tumour suppressor genes

These genes help protect against cancer. They control cell growth. They also repair damage to DNA.

If a cell has a mutation in a tumour suppressor gene, it may lose the ‘brakes’ on its growth. The cell can then multiply out of control.

Some tumour suppressor genes repair damage to DNA. Doctors call them DNA repair genes or caretaker genes.

When there is a mutation in a DNA repair gene, the cell can’t repair damage to itself. So cancer is more likely to develop.

Acquired mutations

Most cancers develop because of gene mutations that happen during a person’s lifetime. Doctors call these mutations acquired mutations.

Acquired gene mutations happen in the part of the body where the cancer later develops. For example, gene mutations happen in the lungs before lung cancer develops.

Many things can cause gene mutations. These include:

• getting older
• things in our environment such as tobacco and sunlight
• our hormones
• our diet.

Doctors call substances that increase the chance of gene mutations carcinogens. Radiation and the chemicals in cigarette smoke are examples of carcinogens.
Usually, several gene mutations must happen in a cell before cancer develops. This can take many years. This is why cancer is more common in older people. Cancers caused by gene mutations that happen during someone’s lifetime are called sporadic cancers.

Genes and inheritance

We inherit our genes from our parents. Everyone has two copies of each gene; one from their mother and one from their father.
Some people are born with a gene mutation that puts them at higher risk of getting cancer. Inherited mutations that make cancer more likely are called inherited cancer genes. Doctors may also call them cancer predisposition genes or cancer susceptibility genes.

If you inherit a gene mutation, it is in all your cells. This includes the sperm cells in men and the egg cells in women. So there is a 50% (1 in 2) chance of passing the gene mutation on to any children.
Inheriting a cancer gene doesn’t mean you have cancer. But, it does mean you have an increased risk of developing certain types of cancer. Further gene changes (acquired mutations) need to happen for a cancer to develop.
Doctors call cancers that develop in a family because of an inherited cancer gene inherited cancers or hereditary cancers.
Inherited cancers often develop at a younger age than sporadic cancers. Most inherited cancer genes don’t increase cancer risk until people are adults. But a few inherited cancer genes increase the risk of cancer in children. We have more information about genetic testing in children.

Can cancer genes ‘skip’ a generation?

Cancer genes cannot ‘skip’ a generation. There is a 1 in 2 (50%) chance of inheriting the gene from one of your parents. So you either inherit it or you don’t. If you don’t inherit the gene, you can’t pass it on to your children. But not everyone with the mutation develops cancer. So it can seem that the cancer skipped one generation.
The gene mutations for female cancers such as breast or ovarian cancer can pass through the father’s side of the family. Men who have the cancer gene for breast and ovarian cancer often don’t develop cancer. But they still have a 50% chance of passing the cancer gene on to their children.
If a daughter inherits a cancer gene from her father and develops breast cancer, it can seem as if the cancer gene has skipped a generation. But this isn’t the case. The mutation can’t skip a generation.

Inherited cancer genes

If a particular type of cancer occurs in a family more than in the general population, some people in the family may have an inherited cancer gene.
Scientists have found inherited cancer genes for some common cancers. These include cancers of the breast, bowel, ovary and womb.
There are other cancers that happen in some families more than usual. These include prostate, pancreatic and testicular cancers. But doctors haven’t found specific inherited cancer genes for these cancers yet.
Sometimes, there are many different types of cancer in a family. Usually, these are sporadic cancers (see above) and are due to risk factors such as age, lifestyle and the environment. But some inherited cancer genes can increase the risk of more than one type of cancer.

When cancers happen together

There are two main patterns where cancers happen together:

• breast and ovarian cancer
• bowel and womb cancer (sometimes with cancers of the ovary, stomach or kidney).

Other rare patterns of cancers can happen.

Low-risk genes

Not all families with more cancers than usual have an inherited cancer gene. But some families may share several genes, which increase their risk of certain cancers. These genes have a weaker effect on the risk of cancer than inherited cancer genes. They are sometimes called low-risk or low-penetrance genes.
Scientists have found several of these genes. But the effect of each gene on its own is small. And there aren’t tests available to check for them. Researchers are trying to find out how these genes interact with other risk factors to affect cancer risk.