Screening for colorectal cancer detects unrecognized disease

November 21, 2008

Screening for colorectal cancer detects four out of ten cancers and should be carefully designed to be more effective, according to a study published today on bmj.com.

About one in 20 people in the UK develop bowel cancer during their lifetime. It is the third most common cancer in the UK and the second leading cause of cancer deaths in Europe and the US.

Previous screening trials have show that faecal occult blood testing can reduce the risk of dying by about 16%. More than 50 countries have introduced screening programmes, but their effectiveness in a public health setting is not clear.

Dr Nea Malila and colleagues from the Finnish Cancer Registry examined whether Finland's national colorectal cancer screening programme could detect unrecognised disease. They studied 106 000 people aged 60󈞬 to test how sensitive screening was in identifying unrecognised disease at three levels—the faecal occult blood test (test to detect small traces of blood in faeces that may indicate disease at an early stage), screening episode, and the national screening programme.

A national screening programme for colorectal cancer began in Finland in 2004 as a public health policy in 22 volunteer municipalities and grew to 161 municipalities by 2006.

Nationally it was decided to split the 106 000 people into two groups—a screening group which received faecal occult blood tests kits by mail and a control group which received the routine health services available in the country.

Anyone whose test indicated blood was contacted so a full colonoscopy could take place.

The researchers found that the sensitivity (accuracy) of the test was 55% when considering cancers that developed after positive tests. The sensitivity from screening episodes was 51% and sensitivity was 38% for the national screening programme.

Roughly, four out of ten colorectal cancers were detected thanks to the organised colorectal cancer screening programme and the researchers concluded that the sensitivity of the Finnish programme was "adequate if relatively low".

The study also presents a model of how to implement a new programme using the principles of experimental design to provide good evidence on effectiveness.

The researchers say: "The sensitivity of the Finnish screening programme for colorectal cancer at the first round was adequate even if relatively low. Programme sensitivity in Finland was sufficient to justify continuation of the programme."

In an accompanying editorial, Joan Austoker and Paul Hewitson from the University of Oxford, say that in addition to programme sensitivity there are other important factors that should be taken into consideration when evaluating a cancer screening programme.

Source: British Medical Journal