Some people have tests for bowel cancer because they have symptoms. Others may not have any symptoms, but have a strong family history of bowel cancer, or have received a positive result from a screening test.
The tests you have to diagnose bowel cancer depend on your specific situation. They may include general tests to check your overall health and body function, tests to find cancer, and tests to see if the cancer has spread (metastasised). Some tests may be repeated during or after treatment to check how well the treatment is working.
Your guide to best cancer care
A lot can happen in a hurry when you’re diagnosed with cancer. The guide to best cancer care for bowel cancer can help you make sense of what should happen. It will help you with what questions to ask your health professionals to make sure you receive the best care at every step.
Read the guide
Your doctor will examine your body, feeling your abdomen for any swelling. To check for problems in the rectum and anus, your doctor will insert a gloved, lubricated finger into your anus and feel for any lumps or swelling. This is called a digital rectal examination (DRE), and it may be uncomfortable, but it shouldn't be painful.
You may have a blood test to assess your general health and to look for signs that suggest you are losing blood in your poo. The blood test may measure chemicals that are found or made in your liver and check your red blood cell count.
Immunochemical faecal occult blood test (iFOBT)
Depending on your symptoms, you may have an iFOBT, which looks for tiny amounts of blood in your faeces. It involves taking a sample of your stools at home, which is examined for microscopic traces of blood, which may be a sign of polyps, cancer or another bowel condition. An iFOBT does not diagnose cancer, but if it finds blood, your doctor will recommend you have a colonoscopy as soon as possible.
Screening test for bowel cancer
Screening is the process of looking for cancer, or abnormalities that could lead to cancer, in people who do not have any symptoms. It is particularly important for bowel cancer, which often has no symptoms in its early stages.
Through the National Bowel Cancer Screening Program, people aged 50–74 are automatically sent a free iFOBT kit every two years. A test kit can also be purchased from some pharmacies. It is very important that you do the iFOBT as it can find precancerous polyps and early cancers in the bowel. Removing polyps reduces the risk of developing bowel cancer, and finding bowel cancer early can greatly improve the chance of surviving the disease.
You can access more information from the Department of Health and the Indigenous Bowel Screen websites.
Screening for people with a higher risk
The National Bowel Cancer Screening Program is for people without symptoms of bowel cancer. If you have:
- symptoms of bowel cancer – talk to your doctor about having a colonoscopy or other tests
- another bowel condition, such as chronic inflammatory bowel disease – talk to your doctor about appropriate surveillance
- a strong family history or a genetic condition linked to bowel cancer – talk to your doctor about when you need to start iFOBTs or screening colonoscopies.
Tests to find cancer in the bowel
Colonoscopy and biopsy
A colonoscopy examines the whole length of the large bowel. It is still possible, however, that small polyps may be missed, especially if they are behind one of the many folds in the bowel or the bowel is not completely empty.
The doctor will insert a colonoscope (a flexible tube with a camera on the end) into your anus and up into your rectum and colon. Carbon dioxide or air will be passed into the colon to make it easier for the doctor to see the bowel.
If the doctor sees any abnormal or suspicious-looking areas, they will remove a tiny sample of the tissue for examination. This is known as a biopsy. During the colonoscopy, most polyps can be completely removed. A pathologist will examine the tissue under a microscope to check for signs of disease and may look for specific genetic changes.
Less commonly used tests
Other tests that may be used to find cancer in the bowel include:
- CT colonography – this uses a CT scanner to create images of the colon and rectum and display them on a screen. It may be used if the colonoscopy was unable to show all of the colon or when a colonoscopy is not safe.
- Flexible sigmoidoscopy – This test allows the doctor to see the rectum and lower part of the colon only. A thin, flexible tube called a sigmoidoscope is inserted gently into your anus and guided up through the bowel. A light and camera at the end of the sigmoidoscope show up any unusual areas, and your doctor can take tissue samples (biopsy).
Before some tests, you will have to clean out your bowel completely to make sure the doctor can see the bowel clearly. This is called bowel preparation or washout. The process can vary, so ask your doctor what you need to do. It’s important to follow the instructions so you don’t have to repeat the test.
- Change diet – A few days before the test, start eating low-fibre foods, such as white bread, white rice, meat, fish, chicken, cheese, yoghurt, pumpkin and potato. Avoid high-fibre foods, such as vegetables, fruit, wholegrain pasta, brown rice, cereals, nuts and seeds.
- Drink clear fluids – Your doctor might advise you to have nothing but clear fluids (e.g. broth, water, black tea and coffee, clear fruit juice without pulp) for 12–24 hours before the test. This will help to prevent dehydration.
- Take prescribed laxatives – You will be prescribed a strong laxative to take 12–18 hours before the test. This is taken by mouth as a tablet or liquid over several hours. It will cause you to have several episodes of watery diarrhoea.
- Have an enema, if required – An enema involves putting liquid directly into the rectum. The liquid washes out the lower part of the bowel, along with any faeces.
If any of the tests above show you have bowel cancer, you will have additional tests to see if the cancer has spread to other parts of your body. These can include:
- CEA blood test – your blood may be tested for a protein produced by some cancer cells.
- CT scan – uses x-ray beams to create detailed, cross-sectional pictures of the inside of your body.
- MRI scan – uses a powerful magnet and radio waves to create detailed, cross-sectional pictures of the inside of your body.
- PET-CT scan – a specialised imaging test that provide more detailed and accurate information about the cancer.
- Molecular testing – if you are diagnosed with advanced bowel cancer, your doctor may order extra tests on the biopsy sample to look for particular features that can cause the cancer cells to behave differently. These tests may look for mutations in the genes or features in the cancer cells suggesting that further genetic testing is required.
Staging and prognosis
Working out how far the cancer has spread is called staging and it helps your health care team decide the best treatment for you. In Australia, there are two main systems used for staging bowel cancer, the Australian Clinico-Pathological Staging (ACPS) system and the TNM (tumour–nodes– metastasis) staging system.
Your doctor will combine the results of your early tests, as well as the tests on the cancer tissue and lymph nodes removed during surgery, to work out the overall stage of the cancer. In general, earlier stages have better outcomes.
Prognosis means the expected outcome of a disease. It is not possible for any doctor to predict the exact course of the disease. Instead, your doctor can give you an idea about the general prognosis for people with the same type and stage of cancer, to help advise you on the best treatment options.
To work out your prognosis, your doctor will consider:
- your test results
- the type and stage of bowel cancer
- the rate and extent of tumour growth
- how well you and the cancer respond to treatment
- other factors such as your age, fitness and overall health.
Understanding Bowel Cancer
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Expert content reviewers:
A/Prof David A Clark, Colorectal Surgeon, Royal Brisbane and Women’s Hospital, and The University of Queensland, QLD, and The University of Sydney, NSW; A/Prof Siddhartha Baxi, Radiation Oncologist and Medical Director, GenesisCare Gold Coast, QLD; Dr Hooi Ee, Specialist Gastroenterologist and Head, Department of Gastroenterology, Sir Charles Gairdner Hospital, WA; Annie Harvey, Consumer; A/Prof Louise Nott, Medical Oncologist, Icon Cancer Centre, Hobart, TAS; Caley Schnaid, Accredited Practising Dietitian, GenesisCare, St Leonards and Frenchs Forest, NSW; Chris Sibthorpe, 13 11 20 Consultant, Cancer Council Queensland; Dr Alina Stoita, Gastroenterologist and Hepatologist, St Vincent’s Hospital Sydney, NSW; Catherine Trevaskis, Gastrointestinal Cancer Specialist Nurse, Canberra Hospital, ACT; Richard Vallance, Consumer.
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The information on this webpage was adapted from Understanding Bowel Cancer - A guide for people with cancer, their families and friends (2021 edition). This webpage was last updated in June 2021.