Risks from colorectal cancer

Although the presenting features of colorectal cancer are well known, the risks they confer are less well defined.

New research published in the open access journal BMC Medicine describes the exact risks posed by eight clinical features for the development of colorectal cancer in a large group of patients.

William Hamilton led a team of researchers from the Universities of Bristol and Birmingham who studied the primary care records of 5,477 colorectal cancer patients and 38,314 controls. He said, "General practitioners (GPs) gain relatively little experience in the diagnosis of colorectal cancer because the incidence is about one per GP per year, and only a proportion of these are diagnosed in primary care. Our findings strengthen the view that rectal bleeding carries a high enough risk to warrant investigation irrespective of other symptoms. Current guidance requires persistence of bleeding for 6 weeks, or accompanying diarrhoea. In our opinion, these additional requirements are unnecessary."

The authors found that the highest risks were conferred by rectal bleeding and change in bowel habit. For men over 60 years, rectal bleeding positive predictive values (PPVs) ranged from 2.4-4.5%. For women, the figures were lower, but still in the 2-3% range. Dr Hamilton added, "Change in bowel habit is less simple: GPs contributing to the database must have been using this term very differently from the separate terms of constipation and diarrhoea, in that the PPVs for change in bowel habit were considerably higher. We cannot know what features led GPs to write change in bowel habit in the notes in preference to the specific motility symptoms - however, from our results it is clear that they were identifying a riskier feature, and one that warrants investigation".

The PPVs of the other presenting features were lower, but still significant. The values for constipation, diarrhoea, abdominal pain and loss of weight were all below 1.5%, confirming that they are low risk symptoms, at any age and in either sex. However, the authors are keen to point out that these are not 'no-risk' symptoms. They say, "The high-risk symptoms of rectal bleeding and change in bowel habit were only recorded in 15.6% and 11.2% of cases, respectively. The remaining majority - with only a low risk symptom - could have their diagnosis expedited in a number of different ways, such as new scoring systems, new biomarkers or measurement of rectal DNA. Without one of these initiatives, or a combination of them, patients with a low risk symptom will continue to be at risk of delayed diagnosis, and possible emergency presentation".