Reduced risk of colorectal cancer in people who have been screened

People with a history of screening for colorectal cancer are 44% less likely to develop the disease in the years following screening than those who have never undergone screening, according to a study published in the Medical Journal of Australia.

Data from participants in the 45 and Up Study, involving 196 464 people from New South Wales who completed a baseline questionnaire distributed between January 2006 and December 2008, found 1096 cases of colorectal cancer (CRC) had accrued in the four years following the baseline survey. Ever having undergone CRC screening before baseline was associated with a 44% reduced risk of developing CRC during the 4-year follow-up period, compared with those who had never been screened.

Additionally, those who reported that they had been screened by a faecal occult blood test (FOBT) had a 40% lower subsequent risk of CRC and those reporting endoscopy screening had a 50% lower risk, compared to people who did not report any CRC screening.

In terms of the subtypes of CRC, the risk reduction was greatest for rectal cancer, followed by distal colon cancer, with the least risk reduction for proximal colon cancer.

"The reduction in subsequent CRC risk in those reporting they had been screened was particularly pronounced for those with a family history of CRC ... compared with individuals without [that history]", the authors, led by Dr Annika Steffen, a research fellow with the School of Population Health at the University of South Australia in Adelaide, wrote, the reason for this is unclear and requires further exploration.

The authors caution against over-interpretation of the findings and note that the study results could not be "directly translated into effectiveness of population screening" due to their observational nature "The results are, however, consistent with those of relevant randomised trials."

They concluded that the study provides data relevant to the real-world application of CRC screening. "The study illustrates a lower risk of being diagnosed with CRC among individuals with a history of CRC screening, compared with individuals who have never had CRC screening, through either FOBT or endoscopy, lasting for at least 4 years after screening."