Diagnosing colon cancer

Written by: Dr John Martin
Edited by: Top Doctors®

Colon cancer develops from polyps in the bowel. We think about 10% of these polyps will progress over the years and grow and develop into a cancer. If you have a colon spill intervention early on, that has two possible outcomes that could be beneficial.

The first thing, obviously, is to find these polyps, which are common and can be removed at colonoscopy, thus doing two things. The first is preventing that polyp becoming a cancer, hence preventing the disease. The second is identifying individuals who are at risk of developing polyps, allowing for further surveillance and further colonoscopies in the future to make sure nothing else develops. If your intervention occurs when you have developed cancer, then early diagnosis is still important.

Colon cancer stages

Colon cancer is basically divided into four stages and your outcome and survival is directly related to the stage of your disease. If you’re diagnosed with bowel cancer at an early stage, then your chance of surviving five years or more is over 90%. If you’re diagnosed at the most advanced or most aggressive stage, survival falls to less than 10%. The survival rate in the second stage is about 70% and the third stage about 40%.


Colon cancer symptoms

One of the problems with colon cancer is that patients with colon cancer can be totally asymptomatic. As a result of this, it is extremely important to take advantage of any screening opportunity that may be available to try and identify either polyps or early cancer because this will improve the potential outcome or prevent development of the disease. If, however, a patient does develop symptoms of colon cancer, the one of the commonest symptoms would be a change in bowel habit towards diarrheoa, either passing more loose stools or more frequent stools. Another common symptom would be blood in the stool. Sometimes the blood is not seen in the stool and as a result, patients can become anaemic and develop symptoms of anaemia such as tiredness. Often, a blood test performed by a general practitioner will show that you’re anaemic with a lack of iron and this again should prompt urgent investigation to look for bowel cancer. Other symptoms can be present such as weight loss, abdominal pain, or a lump in the abdomen. These are much less common.


How is colon cancer diagnosed?

The best test for diagnosing colon cancer would be some form of endoscopic tests: either a colonoscopy or flexible sigmoidoscopy performed by a specialist. These are extremely accurate in making the diagnosis, as the operator is able to see the cancer and take biopsies. which can then be analysed by a pathologist to confirm the diagnosis.

There are other tests such as CT scanning – either an in-depth CT colonoscopy or a normal CT – which can identify abnormalities within the colon, although in this setting, it’s not possible to analyse tissue to confirm the cancer.

There are other tests that can be used to try and identify individuals who are at higher risk of having bowel cancer, such as examining the stool for blood or doing blood tests. It should be noted that these are not in any way sensitive and should not be used to make the diagnosis; rather they should be used to determine if a patient needs a more comprehensive examination.


What is a colonoscopy?

A colonoscopy is an examination of the entire colon using a flexible instrument with a light at the end and a microchip which allows a highly detailed, high definition image to be projected on the screen. This is highly sensitive for picking up abnormalities within the colon, such as polyps or cancers. The preparation for the colonoscopy starts a couple of days before the procedure, when there are some minor dietary restrictions such as eliminating high fibre from the diet. On the day before the procedure, the patient having the examination is allowed breakfast, but after that, no more solid food until after the colonoscopy! However, they are able to drink clear fluids and it is vital to stay hydrated, which helps with preparing the bowel.

The examination may be a little uncomfortable at times, although it should not be painful and is very safe. There is a very small risk of causing some bleeding or a small hole in the bowel, particularly if a big polyp is removed, although this is still an extremely rare complication.


By Dr John Martin

Dr John Martin graduated from Cambridge University and King’s College Hospital, London in 1990 and completed his gastroenterology training within North West London.  He is a highly-experienced gastroenterologist and endoscopist based in London and holds an NHS Consultant post at Imperial College (ICL).  He is an expert in colorectal cancer screening, therapeutic and diagnostic colonoscopy and has 25 years experience of managing all aspects of gastroenterology including abdominal pain or discomfort, reflux disease, diarrhoea and constipation, rectal bleeding, Irritable Bowel Syndrome, Crohn’s Disease and Ulcerative Colitis.

Dr Martin teaches colonoscopy both within the  NHS Trust and also at national screening centres. He is a bowel cancer screening accredited colonoscopist and an examiner for BCSP colonoscopy accreditation.

Dr Martin is Director of the West London Bowel Cancer Screening Centre, he is the national advisor to Public Health England on endoscopy within the Bowel Cancer screening service and chairs the national advisory committee on quality and safety of endoscopy within screening. He forms an integral part of numerous other professional bodies and has been widely published in peer-reviewed journals.

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