Colorectal cancer screening tests

Colorectal cancer (CRC) has increased in recent decades. Screening for CRC is important because it is a disease with a high prevalence and early treatment is beneficial. One study showed that screening tests could save up to 2,400 lives every year in the UK by 2025.

Leading London consultant gastroenterologist Dr Aathavan Loganayagam discusses the different types of colorectal cancer screening options that are available…

What is colorectal cancer?

Colorectal cancer can begin in the colon or the rectum and starts when cells in the body begin to grow out of control. Most colorectal cancers begin as a growth called a polyp on the inner lining of either the colon or rectum. Not all polyps become cancerous but the chance of them developing into cancer depends on their type, whether they are adenomatous polyps (pre-cancerous) or hyperplastic polyps and inflammatory polyps.

Different types of cancer in the colon and rectum:
 

• Adenocarcinomas: make up more than 95% of colorectal cancers.
• Carcinoid tumours: start in the intestine.
• Gastrointestinal stromal tumours: start from specialised cells in the wall of the colon.
• Lymphomas: cancers that usually start in lymph nodes but also in other organs.
• Sarcomas: can start in blood vessels, muscle layers and other tissues.

Slow tumour growth provides a long window of opportunity in which to detect and remove the malignant precursor (the polyp) or detect the cancer at an earlier, more favourable stage: ‘detect the polyp – prevent the cancer.’

Colorectal cancer screening tests

Screening looks for cancer in people with no symptoms and there are tests that find both colorectal polyps and cancer, or tests that mainly find cancer.

Tests that mainly find colorectal cancer
 

• Guaiac Faecal Occult Blood testing – This may reduce mortality from CRC by 15-33%. It looks for hidden blood in the stool through a chemical reaction. The test can be done at home using cardboard sticks provided; the patient must smear two small samples of faeces onto a special screening card, three times over a two week period.
• Faecal Immunochemical test (FIT) – Tests for blood in the stool also using cardboard sticks but the test reacts to the part of the human haemoglobin protein found in red blood cells.
   

Tests that can find both colorectal polyps and cancer
 

• CT Colonography – A recent study showed a 90% pick up of polyps greater than 10mm. This test is an advanced type of scan of the colon and rectum. It takes many pictures unlike a regular X-ray.
• Sigmoidoscopy – A recent controlled study of 170,000 people followed for 11 years revealed a 43% mortality reduction. The doctor looks at part of the colon and rectum using a tube as thick as a finger with a camera, entering into the anus through to the lower part of the colon.
• Colonoscopy – The doctor checks the entire length of the colon and rectum with a colonscope (a lighted tube with a small video camera), similar to a sigmoidoscopy but the polyps are removed. Although it has significant advantages, the test is costly and requires operator expertise.

These procedures are not ideal but the important message of the different ways to screen for colorectal cancer is to ensure that at least one of the options is adopted in order to detect early signs of the disease.