Bowel (colorectal) cancer is the most common cancer affecting both men and women in Australia, with 13 076 cases diagnosed and 4164 deaths reported in 2005.1 It is the second commonest cause of cancer-related death, behind lung cancer. The incidence of bowel cancer increases exponentially after 50 years of age, with a lifetime risk of about one in 17 among men and one in 26 among women.1

Bowel cancer satisfies most of the World Health Organization criteria for population cancer screening.2 Specifically, it is a common, serious cancer, and its natural history is reasonably well understood. It arises from precursor adenomas, and removal of these prevents cancer development. Importantly, most adenomas and early cancers are asymptomatic. Detection at early stages confers an excellent prognosis, and there are numerous tests for early detection and intervention, with the potential to reduce the incidence, morbidity and mortality of the disease.

Cancer screening aims to identify affected individuals who do not suspect they have the disease. This is in contrast to performing diagnostic investigations for symptomatic patients, or targeting individuals with a significant family history of bowel cancer, a history of inflammatory bowel disease, previous adenomatous polyps or previous bowel cancer.

However, bowel cancer screening recommendations can be confusing for medical practitioners. Numerous tests of varying performance levels are available, and it is difficult to separate recommendations for the population from those targeted towards individuals. There are also significant differences between the Australian recommendations endorsed by the National Health and Medical Research Council (NHMRC)3 and two recently published American guidelines, from the United States Preventive Services Task Force (USPSTF)4 and from a collaboration of the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer (representing the American Gastroenterological Association, American Society for Gastrointestinal Endoscopy, American College of Gastroenterology and American College of Physicians) and the American College of Radiology.5 Interestingly, these guidelines differ due to differing interpretations of essentially the same evidence. It is important to note that the newer American guidelines are less relevant to the Australian health care environment, and should not usurp the existing NHMRC recommendations in Australia.

The NHMRC guidelines strongly recommend screening from the age of 50 years, by performing a faecal occult blood test (FOBT) at least every second year. The strength of this recommendation arises from three large, population-based, prospective randomised controlled trials demonstrating a mortality reduction of 15%–33%.3-5 No other cancer screening strategy is based on such strong evidence. Flexible sigmoidoscopy performed 5-yearly receives an equivocal recommendation, whereas colonoscopy and computed tomographic (CT) colonography are not recommended because of insufficient evidence.

In contrast, the American guidelines recommend presenting information to patients, who then choose from the options, including high-sensitivity FOBT, flexible sigmoidoscopy or colonoscopy.4,5 The American recommendations diverge on CT colonography: the USPSTF does not recommend it on the basis of unknown long-term harm,4 while the collaborative joint guidelines endorse 5-yearly examinations.5

Unlike the US, Australia has moved beyond making passive recommendations to become one of a few countries actively implementing a nationwide population-based bowel cancer screening program — the National Bowel Cancer Screening Program (NBCSP) — although, currently, only individuals aged 50, 55 or 65 years are invited to participate (http://www.cancerscreening.gov.au/internet/screening/publishing.nsf/Content/bowel-about). The NBCSP, which uses a high-sensitivity immunochemical FOBT, began in 2006 after a pilot program (2002–2004) found that bowel cancer screening would be acceptable, feasible and cost-effective.6 The age restriction for invitees is part of a phasing-in process designed to enable resources to cope with increased downstream demand, especially for colonoscopy, which is the recommended investigation for participants with a positive FOBT result. About 7.5% of NBCSP participants have a positive FOBT result, and 5% of these are found to have cancer.7 Although the federal government has made no commitment to the NBCSP beyond June 2011, it is inconceivable that the program will simply be terminated, given the strong evidence basis for its function.

The problem facing Australian medical practitioners is what to do in the face of the various disparate guidelines. A simple approach is to recommend participation in the NBCSP for all invitees. Increased awareness of bowel cancer will also cause some individuals outside the eligible ages to enquire about screening. In these cases, the NHMRC recommendations are most appropriate: for medical practitioners wishing to encourage opportunistic screening, an immunochemical FOBT can be recommended for patients aged between 50 and 75 years. Patients with positive FOBT results will then require follow-up colonoscopy.

However, these recommendations ignore the growing tendency, often driven by patients, for screening with colonoscopy. In the absence of symptoms, about 500 colonoscopies need to be performed on 50–75-year-olds to identify one cancer,7 with an associated one in 1000 risk of serious complications.8 This contrasts with one cancer found for every 20 colonoscopies in the NBCSP.7 Of course, many patients will have premalignant adenomas that would be found with colonoscopy screening, which in turn creates a substantial requirement for long-term surveillance colonoscopies. Yet the vast majority of patients with adenomas will never develop bowel cancer, even without future intervention.9 Finally, the imperfections of colonoscopy are becoming increasingly recognised, reducing the ratio of its potential benefits to high cost.10,11 Thus, “indiscriminate” use of colonoscopy diverts availability of this expensive resource away from those most in need of it, especially in the public health system.

As a step towards improving colonoscopy access, the Western Australian Department of Health will introduce a Colonoscopy Services Model of Care, scheduled for implementation over the next 2 years in the public hospital system, that prescribes appropriate use and referral processes. This will be supported by trained clinical staff and computerised referral systems to improve the quality and triaging of referrals in the public sector. Patients will also be informed of the priority level of their case, and the appropriate waiting time. Other states in Australia should strongly consider implementing similar strategies.

Bowel cancer is common, serious and largely preventable. Medical practitioners should be encouraged to refer individuals for bowel cancer screening in compliance with the current Australian NHMRC recommendations and the NBCSP. Such practice will ensure that colonoscopy resources are available to those most in need in our community.