Family doctor

Colorectal cancer screening

Colorectal cancers (cancers of the colon and rectum) are an important cause of morbidity and mortality in New Zealand. Each year approximately 2500 people develop colorectal and 1100 people die of the disease. These figures give New Zealand among the highest incidence and mortality rates of colorectal cancer in the world. (ref1.).

Earlier diagnosis of colorectal cancer improves survival, so for this reason international interest in effective colorectal cancer screening programmes has been growing.

Screening involves testing people with no symptoms to identify early signs of disease.

A recent review found that screening using faecal occult blood tests (FOBTs) is likely to avoid approximately 1 in 6 colorectal cancer deaths (ref 2). Screening using FOBT does nothing however to reduce the likelihood of someone developing colorectal cancer.

Colorectal cancer screening programmes abroad

Many countries (including the UK and Australia) have set up colorectal cancer screening programmes: In the UK, the current screening programme uses FOBT, and is offered to patients in their 60s every two years. In Australia, people aged over 50 years are eligible to participate in the screening programme every two years, and are sent a pre-invitation letter followed by an invitation pack, including an information booklet and an FOBT kit, in the mail. Those who choose to participate complete the FOBT in their own homes and mail it to the pathology laboratory, where the test is analyzed.

Is there a colorectal cancer screening programme available in New Zealand?

Currently in New Zealand there is no colorectal cancer screening programme running. In 2005 the National Screening Unit of the Ministry of Health appointed a Colorectal Screening Advisory Group to provide independent strategic advice and recommendations on population screening for colorectal cancer in New Zealand. There are concerns about adding screening into a system which currently has some public hospitals already struggling to deliver timely diagnostic or surveillance colonoscopy.

In 1997, in response to some overseas trial results showing benefit in screening with FOBT, a working party was established by the New Zealand National Health Committee to make recommendations on the advisability of introducing a publicly funded screening programme based on FOBT screening. This working party did not recommend an FOBT-based population screening programme for colorectal cancer because of the “modest potential benefit, the considerable commitment of health sector resources and the small but real potential for harm”.(ref 3)

 What is a faecal occult blood test (FOBT)?

A FOBT is a test that requires a patient to collect a small amount of faeces (bowel motion) which is then analyzed by the medical laboratory to detect the presence of blood. The presence of blood in the faeces may indicate the presence of a cancer.

There are two main types of FOBT - immunochemical tests and traditional chemical (guaiac) tests.

Guaiac FOBTs are currently used in the UK  (and are the ones available in New Zealand although not used all that often)  require a person not to consume red meat, specific fruit and vegetables (for example, raw broccoli,) vitamin C supplements, aspirin or anti-inflammatory drugs for three days prior to taking the first test sample and throughout the testing period.

The immunochemical FOBT is used in the Australian screening programme as the preferred testing method, in contrast to the guaiac FOBT, as it has no restrictions on diet or medication. It is a more expensive test.

A current review of these FOBTs has shown that immunochemical based tests are more sensitive than guaiac based tests.

Should New Zealand GPs order FOBTs?

When a patient presents to a GP with abdominal symptoms or an iron deficiency anaemia several different diagnoses are usually considered (such as colorectal cancer, irritable bowel syndrome, coeliac disease, menstrual-cycle related problem). The GP has to then try to identify the patients who should be referred for further investigation to assist with diagnosis.

At present, GPs are advised that FOBTs should not be part of a diagnostic investigation for clinically suspected colorectal cancer (reflected in UK’s National Institute for Health and Clinical Excellence (NICE) guidelines on cancer referral). This means that if a patient has symptoms or signs that are suggestive of colorectal cancer then a GP should go ahead and refer for other investigations that would assist in diagnosis, but not to rely upon a FOBT result. This is because there is a possibility of false reassurance, as FOBTs can miss some colorectal cancers.

In other words, while FOBTs may be useful in screening the asymptomatic population, they should not be relied upon to rule out problems in symptomatic patients who may need further other tests, depending on their age and symptoms

What happens if a FOBT is positive for the presence of blood?

If a FOBT is performed and the result is positive, the patient is then referred to have the bowels examined closely with further diagnostic tests  ( e.g colonoscopy, flexible sigmoidoscopy, double-contrast barium enema), but these tests can often cause discomfort and can occasionally cause serious adverse consequences. It is important for patients to know that blood identified in the faeces may be due to several reasons and not just cancer.

What other tests are there being used in screening trials?

The results of a 16 year study have recently been published in The Lancet (ref4)  showing that a one-off  single flexible sigmoidoscopy examination in men and women aged between 55 and 64 reduces the incidence of bowel cancer by a third and bowel cancer mortality by 43%, in comparison with a control group . The study showed  that to prevent one cancer 191 patients must be screened by sigmoidoscopy and that for every 489 people screened one life would be saved. But she said she expected the benefits to prove even greater with even longer follow-up.

This benefit compares very favorably  with other screening programmes eg cervical and breast cancer screening .

Some UK cancer experts think that the current colorectal cancer screening programme in the UK should include a single sigmoidoscopy examination in addition to the current FOBT.

A sigmoidoscopy is an examination of the lower part of the bowel, whereby a short tube is inserted in the patient’s anus (bottom) and the doctor can look for any growths that are suggestive of cancer or pre-cancer. Two thirds of colorectal cancers and adenomas occur in the lower part of the bowel.

During sigmoidoscopy any small polyps found are removed straight away, as they can become cancerous if left untreated. Patients are referred for colonoscopy if any polyps are considered to be high risk—usually if they are over 1 cm in size, for example.

Colonoscopy is an examination of the whole bowel and is a longer procedure that would not be as suitable for population screening, although it may be a better investigation for some- eg positive family historyof bowel cancer , known polyps or genetic concerns.

The future.

The delay in the development of a colorectal screening programme in New Zealand does allow the review this latest research and may promote a move towards the use of one-off flexible sigmoidoscopy as the preferred screening test for a national programme. Whereas the FOBT test may detect a cancer that is bleeding, flexible sigmoidoscopy can detect cancer and preinvasive polyps, whether or not they are bleeding, in that part of the colon and rectum where the disease is most common. Therefore, unlike the FOBT test, flexible sigmoidoscopy reduces both the incidence and mortality from bowel cancer.

References

1. Ministry of Health. Cancer: new registrations and deaths 2002. Wellington: Ministry of Health, 2006

2. Hewitson P, Glasziou PP, Irwig L, Towler B, Watson E. Screening for colorectal cancer using the faecal occult blood test, Hemoccult. Cochrane Database of Systematic Reviews 2007, Issue 1. Art. No.: CD001216. DOI: 10.1002/14651858.CD001216.pub2

3. Colorectal Cancer Screening Working Party. Population Screening for colorectal cancer. Wellington: National Health Committee, 1998. http://www.nhc.govt.nz/publications/colorectal.htm

4. Atkin W, Edward R, Kralji-Hans I. et al. Once-only flexible sigmoidoscopy screening in prevention of colorectal cancer: a multicentre randomised controlled trial. Lancet, Vol 375,Iss 9726.May 2010. Pg 1624-33

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)60551-X/abstract