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How is cancer detected?

Screening can detect early signs of cancerCancer is easier to treat and cure if it is diagnosed early. So a huge amount of effort has gone into developing ways to detect early signs of the disease. 

On this page you can read about some of the methods that doctors use to find out if someone has cancer.

There is more information about the different tests used to detect cancer on our CancerHelp UK website.


Imaging techniques enable doctors to create detailed pictures of what's going on in our bodies without having to open us up. Here are some of the techniques commonly used to diagnose cancer.

  • X-rays are a form of electromagnetic radiation that can be used to take photographs of the inside of your body. X-rays are absorbed by dense materials inside the body, such as cartilage and bone, but not by lighter substances like blood. Read more about X-rays on CancerHelp UK
  • CT scans (or CAT scans as they are sometimes called) take lots of different x-ray photos of your body from different angles. These are then put back together using a powerful computer to form a 3D image or a series of pictures of 'slices' through your body. This allows doctors to see exactly where a tumour is. Read more about CT scans on CancerHelp UK
  • MRI scans (Magnetic Resonance Imaging) use magnetism rather than x-rays to build up a picture of the inside of your body. They can be used like a CT scan to view 'slices' through the body, or can make 3D images of your organs. MRI scanning usually produces a more detailed view of the body than x-rays, so doctors often use it to examine the brain. Read more about MRI scans on CancerHelp UK
  • PET scans (Positron Emission Tomography) are relatively new technology, and is only available in a few hospitals in the UK at the moment. PET scans can be even more sensitive than MRI and x-rays, and they can show how a particular bit of your body is working, not just what it looks like. Cancer Research UK has been leading the way in developing PET scanning in Europe. Read more about PET scans on CancerHelp UK
  • Ultrasound scans use sound waves to build up a picture of the inside of your body. Read more about ultrasound on CancerHelp UK



An endoscope is a long, thin flexible tube with a camera and a light on the end. Doctors can use this to look inside parts of your body to see if there is anything unusual.

Sometimes the endoscope is inserted into a body cavity such as the anus or gullet; in other situations the surgeon may have to make a small incision through which to insert the endoscope, for example to examine the abdominal cavity.

An endoscope can also be used to take samples of any abnormal tissue.

Tissue samples

The only absolutely certain way to diagnose cancer is to take a cell sample (a process called a biopsy) and look at it under a microscope. This is usually done by placing a needle into the affected area and sucking out some cells.

Doctors hope that one day, by taking a cancer biopsy and analysing the different genes that are active in the cancer cells, they may be able to work out very quickly how best to treat you - this is known as personalised medicine. Cancer Research UK is actively funding many research programmes that aim to do exactly this, such as the work of Professor Carlos Caldas and his team in Cambridge.

Tests on blood and other samples

There are a number of blood tests that aim to diagnose cancer by looking for tell-tale molecules. These can include sugars, fats, proteins and DNA

For example, the PSA test - which measures the level of a protein called PSA in a man's bloodstream - can be used to diagnose and monitor prostate cancer. And measuring the levels of a molecule called CA125 in the blood can reveal whether a women might have ovarian cancer. Cancer Research UK-funded scientists are currently testing whether this test - along with ultrasound scanning - is suitable for a national ovarian cancer screening programme.

Cancer Research UK scientists are also working on ways to test urine or other body fluids for the presence of a protein called MCM5, which can reveal cancer. The main issue with such tests is that there must be a clear difference between normal and cancerous samples. 

In the future, these tests may become even more sensitive. Professor Caroline Dive and her team at the University of Manchester are measuring individual cells and DNA from tumours in the bloodstream of cancer patients. At the moment, they are using the technique to tell how patients are responding to treatment. But in the future this could lead to more effective ways to diagnose cancer earlier.

Cancer screening

Cancer screening detects cancers when they are at an early stage, or - in the case of cervical cancer screening - before they have developed. 

We know that screening saves thousands of lives each year. In the UK, we have three national screening programmes - for breast, cervical and bowel cancers. 

In April 2010, we helped to fund an important breakthrough in bowel cancer screening, using a technique called Flexi-Scope. And in October 2010 the Government committed to incorporating this more effective type of screening into the NHS screening programme. 

Find out more about cancer screening.

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Question about cancer? Contact our information nurse team
Updated: 16 November 2009