Summary

Researchers in Norway report from an ongoing study designed to examine the benefits of screening for colorectal cancer. One group had flexible sigmoidoscopy, the other did not. At seven years, no difference in incidence of cancer was found between the two. However, there was a trend towards reduction in mortality from colorectal cancer with screening. It may be several more years before the benefits of colorectal screening can be fully assessed.

Introduction

Screening for colorectal cancer among those over 50 is thought to reduce the incidence of this common disease among the population. Screening is done in the US and is being introduced in the UK, involving either fecal occult blood testing or colonoscopy (or both). If pre-cancerous polyps are found, then they are promptly removed before they can develop. However, research is ongoing into the precise impacts of colorectal screening so that policy makers can decide how often screening should be done and what the cost benefit is to health systems.

What was done

Researchers at the Norwegian Colorectal Cancer Prevention Center studied a group of 55,736 men and women aged 55 to 64 from Oslo and Telemark county. They were either offered flexible sigmoidoscopy or no screening and tracked through the cancer registry for an average of seven years. Flexible sigmoidoscopy uses a flexible tube to examine the large intestine for early signs of cancer like polyps. This study is ongoing and will report again after a longer follow up time.

What was found

There was no difference, at seven years, in incidence of colorectal cancer between the screening group and the non-screening group. In the screening group as a whole there was a 27% decrease in colorectal mortality, but this was not statistically significant. But this result was diluted by the effect of those invited for screening, but not attending. For those who did attend, total colorectal cancer mortality went down by 59% which is statistically significant.

What this study means

The benefit from colorectal screening by flexible sigmoidoscopy was not as great as might have been expected. But it did save lives and it may be that pre-cancerous lesions take longer to develop than previously thought – meaning that longer follow up will show more benefit in terms of decreased incidence of colorectal cancer.

Source

Hoff G, Grotmol T et al Risk of colorectal cancer seven years after flexible sigmoidoscopy screening BMJ online 2009;338:b1846