Understanding cancer

What is cancer?

Our bodies are made up of billions of tiny parts that fit together like building blocks. These parts are called cells.

Healthy cells grow, divide and eventually get worn out and die. This cycle usually continues without any problems.

Cancer happens when something goes wrong with the cell and it grows and divides in an uncontrolled way. Cancer cells divide too much and don’t die in the way normal cells do. These cells can form a lump called a tumour.

A tumour can form inside:

  • an organ (part of the body that does a specific job, such as the liver or kidney)
  • a bone
  • the lymphatic system (a network that helps defend your body from disease) – when a tumour forms here, it is called a lymphoma.

If the cancer affects your blood, the cancer cells do not form a tumour but affect the bone marrow (the spongy centre of your bones where your blood cells are made). This type of cancer is called leukaemia.

Cancer cells from a tumour can spread to other parts of the body. That is why having treatment as soon as possible is important.

There are more than 200 different types of cancer. Each type has its own name and treatments. People with cancer need to have tests to find out exactly what type of cancer they have, and to find out whether it has spread. This helps the doctors plan the right treatment for each person.

How did you get cancer?

Scientists are finding out more about cancer all the time. But we still don’t always know why people get it. Particularly when you are a teenager or in your 20s, cancer is something that can just happen without a reason.

One thing we definitely know is that cancer is not a disease you can catch from someone else – it is not infectious.

You may worry that the cancer could be linked to things you have done – for example, smoking, drinking or taking drugs. But this is very unlikely when you are young.

Some cancers can be caused by inherited faulty genes. This means that the cancer is passed on from one generation to another (inherited). If this is the cause, it is likely that other members of your family will have had similar cancers in the past. But most cancers are not caused by inherited cancer genes. Doctors think that only 2 or 3 in every 100 cancers may be an inherited cancer.

An animated image of cells forming a tumour.

What is cancer?

Watch our animation about how cancer starts in our cells.

About our cancer information videos

What is cancer?

Watch our animation about how cancer starts in our cells.

About our cancer information videos

Questions you might want to ask about cancer

Here are some questions you might want to ask your doctor or nurse.

  • Where is the cancer?
  • What caused the cancer?
  • How serious is it?
  • Can it be treated
  • Can it spread?
  • Where could it spread to?
  • What happens if it spreads?
  • Could I have inherited the cancer from someone in my family?

Different types of cancer

Cancer in teenagers and young adults is quite rare. Most cancers are diagnosed in people aged over 65. Although there are over 200 different types of cancer, certain cancers are more likely to affect teenagers and young people. Some of these are:

Back to Teens and young adults

Finding out you have cancer

It can be hard to know what to tell people about the cancer, and it’s normal to have lots of different feelings.

Cancer types

Find information about the cancer types that are most likely to affect teens and young adults.

Tests and scans

Find out about some of the tests and scans that are used to diagnose cancer and to see how you're doing during and after treatment.

Cancer treatment

Find out about the possible treatments for cancer. We have info about when each treatment might be used, how it's given and possible side effects.

Relationships, sex and fertility

During or after treatment, you may worry about whether the cancer and its treatment will affect your relationships, sex life or fertility (ability to have children).

After cancer treatment

This section is about some of the physical, emotional and practical issues that might affect you after you've finished your cancer treatment.