A small number of colorectal cancers was detected in a group of subjects three years after a negative screen.

Screening for cancer by examination of the rectum and colon should be done every five years, if the first exam shows no problems. But polyps and even cancers can occur during the five year interval, according to researchers at the University of Pittsburgh.

They looked at participants in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial, screening them at the start and three years later. Of those who tested negative at the start, 13.9 per cent developed a polyp or mass by the time of the three year screen. A few of these were cancers; the researchers conclude that there is a 0.8 per cent chance of colon cancer developing in the three years after a negative screen. On its own, this study does not justify a recommendation for more regular screening, of course. It may be more important to get more people along for their five years screens in the first instance.

Source

Journal of the American Medical Association 2nd July 2003