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Bowel cancer guidance ‘no better than chance’ in under-50s

By Lilian Anekwe

The NICE guidance on which patients to refer for suspected cancer perform ‘no better than random chance’ in patients under 50, and is a poor discriminator of bowel cancer symptoms, according to leading UK cancer researchers.

Despite introduction of a national screening programme in England for those aged 60 to 69, the majority of cancers continue to be diagnosed clinically by GPs because most cancers occur after this age, some people decline screening, and screening does not detect all cancers.

But the symptoms are also features of more common and benign conditions, and a typical full-time GP will diagnose only one new case of colorectal cancer a year.

Researchers investigated three different colorectal cancer scoring systems – the Bristol Birmingham equation (BB) – derived from a large primary care dataset – the CAPER score – derived from a primary care case-control study – and a symptom score derived from NICE guidance on the urgent referral of patients with suspected cancer.

The researchers tested the BB equation by selecting READ codes for 24 clinical features of colorectal cancer, and then used a multiple logistic regression to calculate a score equal to the symptom’s odds ratio.

Patients with a positive faecal occult blood test, an abnormal rectal examination or an abdominal mass who would always qualify for further investigation were allocated an arbitrary maximum score of 100 points.

The CAPER scores were derived from the presence or absence of six features of colorectal cancer: constipation (25 points), diarrhoea (10), loss of weight (20), abdominal pain or tenderness (15), and one laboratory finding of low haemoglobin (either 20 or 30 points depending on haemoglobin levels).

Patients in the NICE dataset were assigned a score of 100 points for abdominal mass, positive faecal occult blood test or abnormal rectal examination for consistency. One point was assigned for individual features for which urgent referral is recommended by the NICE guidance.

Researchers estimated the yield of colorectal cancers using these symptoms by calculating and comparing positive predictive values. Overall, they identified 5,477 cases and 38,314 controls in a total of 317 practices, with a mean age of 70.6 years.

They then measured the sensitivity and positive predictive value of each tool. Interpretation of the NICE guidance had a positive predictive value of 3.1% at age 70-74. The CAPER and BB tools for the same age had a positive predictive value of 3.3% and 3.7%, respectively.

Writing in the journal Gut, the researchers concluded: ‘In both datasets the overall discrimination characteristics of the BB equation were consistently better than those of the CAPER score and both were superior to any of the interpretations of current guidance. NICE guidelines performed no better than chance in subjects aged under 50.’

Dr Marshall said NICE guidelines may perform less well because they include fewer predictor variables, some of which only apply at certain ages.

Constipation, loss of weight and abdominal pain are all absent from NICE guidelines, while diarrhoea, rectal bleeding and anaemia have an age restriction within NICE.

‘This means that NICE guidelines perform well for the minority of colorectal cancers with typical features, but less well for the majority of cases with low risk symptoms.

‘One criticism of NICE guidance is that only the minority of patients with colorectal cancer have a high risk symptom before diagnosis, with the majority experiencing constipation, diarrhoea or abdominal pain, or a combination of these. Thus, it is not surprising that NICE fails to identify such patients, and that survival from colorectal cancer has improved little since they were published.’

The NICE guidance on suspected cancer was published in 2005 and is under currently under review. A spokesperson for NICE admitted the guidance lagged behind the latest evidence ‘in relation to the signs and symptoms and initial investigations of colorectal cancer.’ He added: ‘This study will be considered as part of the review.’

Bowel cancer guidance ‘no better than chance’ in under-50s