Diagnosis of colorectal cancer in primary care: the evidence base for guidelines.

Colorectal cancer is common, causing approximately 11% of cancer deaths in the UK. However, a GP would only expect to see one new presentation each year. Referral guidelines outlining clinical scenarios of high risk have been published. These aim to help GPs select patients for rapid investigation. The purpose of this study was to review the presenting features of colorectal cancer in primary care, using the basic structure of the UK Referral Guidelines for Suspected Cancer. A structured literature review was carried out. Two symptoms have a high predictive value for cancer: rectal bleeding and change in bowel habit towards increased looseness or increased stool frequency. Other symptoms, such as abdominal pain, are so prevalent in the community that they have little predictive value. There is little published evidence on abdominal or rectal masses and iron deficiency anaemia as presenting features for colorectal cancer. However, these are so likely to have an important cause, investigation is mandated. Two areas in the Referral Guidelines are questioned: the need to defer investigation of change in bowel habit towards increased looseness or increased stool frequency for 6 weeks, and the low risk nature of constipation. The Referral Guidelines have a reasonable evidence base.