Colorectal cancer in primary care
Authors: David Weller
Journal: BMJ (2006)

Primary care has a substantial role in reducing the public health burden of colorectal cancer. Given that mortality from colorectal cancer increases with more advanced disease at diagnosis1 and that most patients present with symptoms that prompted them to consult their general practitioner,2 both patients and doctors need to recognise the symptoms that suggest a high risk of cancer.

In this week's BMJ du Toit and colleagues report a 10 year prospective study which confirms the importance of rectal bleeding as an indicative symptom for colorectal cancer.3 The study found that about one in 10 patients with new onset rectal bleeding had cancer. The authors say that general practitioners should investigate anyone aged 45 years and older who presents with rectal bleeding, with or without a change in bowel habit.

Lower gastrointestinal symptoms are common in general practice but largely non-specific,4 and general practitioners face considerable challenges in determining which symptoms warrant urgent attention. The evidence on rectal bleeding varies according to the setting and design of studies, and treating all cases as potential colorectal cancer may lead to many unnecessary investigations.5

Yet current patterns of practice need to change. We know, for example, that standard guidance is insufficient to ensure the best use of urgent referrals.6 A promising development is the use of diagnostic algorithms based on symptom scores, which can guide clinicians in interpreting various combinations of symptoms and patients' characteristics.7 These techniques need refining using data from primary care populations that have not been referred to specialists. We also urgently need studies examining whether incorporating estimates of quantitative risk into decision making on cancer referral can work—in the same way that estimating cardiovascular risk is now routine in primary care.

To reduce the future burden from colorectal cancer, primary care must engage with a range of strategies beyond symptom based early diagnosis. The UK government has decided to introduce screening in England based on the faecal occult blood test. Evidence supporting screening for bowel cancer is convincing,8 and the UK pilot study has shown that screening is feasible in the general population, with acceptable rates of uptake and detection.9 The programme is being rolled out (albeit more slowly than expected10), and recruitment and follow-up will be organised centrally, although some of the workload (such as meeting patients' information needs) will spill over to primary care.11 Other countries such as Australia are similarly committed,12 though with less central coordination. The US government favours an unregulated approach in which screening by faecal occult blood testing is often bypassed for more definitive tests such as colonoscopy.13

In England general practitioners will need to correct patients' misunderstandings about bowel cancer and to emphasise the low sensitivity of the faecal occult blood test. The programme in England is targeting 60-69 year olds initially (based largely on arguments of cost effectiveness and higher yield). Those working in primary care will inevitably deal with patients on either side of this narrow age window asking about symptoms and requesting screening, and will probably field more inquiries about dietary factors such as fibre and fruit consumption.14 Furthermore, ongoing effort will be required to maintain participation rates close to 60%, and this will be strongly influenced by information received in primary care.11

Perhaps most importantly, many people invited for screening will have symptoms, and they may believe that taking a screening test precludes the need to have those symptoms investigated further. On the contrary, rigorous symptom based diagnosis will still be vital in reducing rates of missed and interval cancers, and cancers in non-participants.

The paper by du Toit and colleagues3 adds to a growing body of evidence that we need to investigate new onset rectal bleeding effectively. Further studies should refine existing guidance on rectal bleeding and other gastrointestinal symptoms. Consideration of the specific characteristics of rectal bleeding may, for example, have the potential to improve the sensitivity and specificity of referral to specialist care.14

A consistent message from available evidence is that general practitioners should treat rectal bleeding with a high index of suspicion, take into account other factors related to patients and not be distracted by the presence of haemorrhoids or other pathology unrelated to cancer. They will also have an increasingly important role in educating patients about responding to symptoms in the context of a screening programme.