What are cancer genes?

Callum Campbell

You might have heard of cancer genes in the news every now and then – maybe in headlines like ‘Could cancer genes hold the key to a cure?’ or some other exciting tag. Cancer genes might sound very sciencey and complicated, but really they aren’t so bad. Let’s take a look at what cancer genes are and what they mean for cancer research today!

Cancer

Cancer comes about when a healthy cell (which can divide), changes suddenly from doing its normal job, to having only one function – growth and division. Growth and division is a tightly controlled process in healthy people. Why? To make sure our body parts don’t become too small or too big – imagine if your brain suddenly grew too big to fit in your skull, for instance! When a new cancer cell divides and grows uncontrollably, it becomes a big lump of cells called a tumour, which can squash and damage the healthy cells around it.

Cancer genes

You have many different types of gene in your body, controlling everything from how to produce digestive juices in the stomach, to how to grow a toenail. Only some genes, however, are relevant to cancer. These are cancer genes. In a healthy person, cancer genes actually protect you from cancer by controlling cell division. If cell division is properly controlled, cancer cannot develop.

There are two types of cancer gene that do this – oncogenes and tumour suppressor genes (TSGs). Oncogenes are the accelerator pedal on cell division. TSGs are the brakes. Usually, oncogenes and TSGs balance each other out nicely.

Caretaker genes are another type of cancer gene. They work like a bit like a shield to protect your DNA from getting damaged, which also prevents cancer.

How do cancer genes cause cancer, then?

Cancer genes only cause cancer if they become damaged and stop working properly. This can happen in three ways:

• If a TSG is damaged, it may become permanently ‘off’ or broken, like the brakes getting cut on cell division. This causes cancer. Since you have a spare copy of every gene (one copy from mum and one from dad), a cancer can only come about if both copies of a TSG get knocked out.
• If an oncogene is damaged, it may become permanently ‘on’ or active, like the accelerator pedal getting stuck to the floor. This is called an activating mutation, and only needs to happen once to cause cancer.
• If a caretaker gene gets mutated, the shield is broken and all your DNA is at increased risk of damage. Without the caretaker genes to protect them, TSGs and oncogenes can easily lose their function, leading to cancer.

Cancer susceptibility

In some cases, cancer genes are passed down through families. These genes don’t work properly in the first place and are called cancer susceptibility genes. Fortunately these are quite rare.

For example, if the inherited useless gene was supposed to be a TSG (remember, the brakes!), you’d only have one working TSG left. If this one got damaged, there would be no backup and a cancer would develop. People who inherit these genes are more likely to get cancer at a young age or to get multiple cancers.

Using cancer genes to treat cancer

The genes in your body code for unique characteristics (e.g. blue eye genes for blue eyes). Just like this, mutated cancer genes code for unique markers on cancer cells, such as receptors and proteins. These markers provide a target for cancer treatments to lock onto – this is why we call them targeted therapies.

When we figure out which cancer genes have been mutated, we can use this information to create new targeted therapies against their proteins. When the new drug hits its target, the cell will either die or be destroyed by the immune system. A very real example of this is Herceptin. Herceptin is a targeted therapy that can treat some breast cancers by latching onto the unique HER2 molecule on the cancer cells – a molecule which is there in the first place because of an oncogene!

Making these new targeted therapies is the most exciting part of cancer genes in research, and who knows, maybe one day it could hold the key to a cancer cure.