What is cancer?

About half of all people in the UK will develop cancer at some point in their lives. Cancer is not one disease, but the name for a group of very similar diseases. There are over 200 different types of cancer, and although each type is similar in many ways, there are also many differences between the types depending on where in the body the cancer started growing.

When we are made we come from one cell, an egg that is fertilized by a sperm. This cell splits into two (divides), to make two cells, and then those two cells split again to make four cells. The cells keep on dividing until they make up all the different bits in our bodies, such as our bones, blood, skin and organs. As we grow, cells keep on dividing and increasing in number to replace old cells or repair cells that have been damaged.

Our bodies are made up of millions of tiny cells and they have different jobs. For example, the job of some cells is to make our heart, whilst the job of other cells is to live in our blood and fight illness. Normally cells only divide and produce more cells when they are needed for the body to grow or to keep healthy.

Cancer is caused by cells in our bodies dividing in an uncontrolled way so that they no longer do their jobs. This can happen when genes that are inside the control centre in our cells are damaged in some way. All cells have a control centre and inside there we have genes that are responsible for telling the cell what to do. When a gene is damaged (we call this a mutation) the cell starts behaving in an uncontrolled way and keep on dividing when it should have stopped, actually a damaged cell should normally die. And if abnormal cells keep on dividing instead of dying, they create more cells that are also abnormal because they have the same gene fault.

It’s important to know that not all gene damages develop into cancer cells as normal cells can repair such damages or the damaged cell can die without starting to divide in such an uncontrolled way.

However, sometimes the damaged cells are not repaired and they don’t die and instead the abnormal cells keep on dividing and become cancerous. Because we talk about genes being damaged, it’s easy to think that means cancer is inherited as we often talk about genetic diseases. And it can happen that people inherit faulty genes from their parents, but that only means that they have a higher risk of getting cancer - it doesn’t mean that they will definitely develop cancer. That's important to know. In most cases though, when people get cancer the damage in the gene is not inherited but it has happened by mistake when the cell was dividing. We don’t know everything about why genes in normal cells sometimes get damaged when they divide, but we definitely know that things like cigarette smoking and sun exposure can damage genes inside cells so they start growing out of control.

The uncontrolled cell division creating a cancer can start in any part in the body, which is one reason why there are so many different types of cancer. Most often, the cancer cells create a lump but they can also circulate and build up in the blood and in the bone marrow.

Another thing that make cells cancerous besides growing out of control, is that they can also grow into other tissues nearby and they can travel via the blood and lymph vessels to other parts of the body. Normal cells don't do that. When normal cells drift away from where they're supposed to be, they get instructions to die ('cell suicide') to prevent cells from growing in the wrong place. Unfortunately, cancer cells sometimes don't get that instruction or they don't follow the instruction and are therefore able to move around the body and cause cancer to grow in other places in the body, often far from where the cancer originally started. Cancer tumours that grow away from where they started are called secondary cancer or metastasis. Sometimes people say that they have secondaries or that the cancer has metastasised and that means that the cancer has spread and started growing in a different place from where it originally started. It's still the same cancer though. So, for example if a breast cancer has spread to the lungs and the bones, the person doesn't have three different types of cancer but breast cancer that has metastasised to the lungs and the bones. (Or said differently, breast cancer with secondaries in the lungs and bones). The earlier a cancer is discovered the better is the chance of treating it and prevent it from spreading to other places in the body.         

Important to know is that different types of cancer can behave in very different ways and therefore they need different treatments that are specifically developed to kill the cancer cells that are the cause of each specific cancer.

To help you find out more, we have linked to Maggie’s CancerLinks where you will be signposted to high quality information about what cancer is and how it develops.

Please get in touch with us if you have any worries or questions about cancer.

Page updated 5 July 2017