Australians who participate in routine colorectal cancer screening almost halve their risk of developing the disease over four years compared to those who don’t take up screening invitations, a new analysis reveals.

The research, involving nearly 200,000 people from NSW who were part of the 45 and Up Study, found that people who were screened for colorectal cancer (CRC) reduced their risk of developing the disease by 44% in the next four years compared to those who had not been screened.

The reduced risk was more pronounced for rectal and distal compared to proximal cancers.

Difficulty in detecting precancerous lesions in that region may come down to quality of bowel preparation before procedures, the limited scope of endoscopies in being able to extend all the way up to the colon and FOBT not being able to detect altered blood from lesions located higher up the colon, the authors suggested.

Though not statistically significant, the effect was greater in people who had been screened using endoscopy compared to those who had undergone FOBT. Reductions in CRC risk were about 40% for FOBT and 50% with endoscopic procedures.

Lead author Professor Emily Banks, scientific director of the NSW 45 and Up Study and NHMRC Senior Research Fellow at the National Centre for Epidemiology and Population Health at the Australian National University, said that for GPs, this was another piece of evidence they could pass on to patients informing them about what they can expect following bowel cancer screening.

“The evidence to date is that if you do the FOBT, have all the relevant follow-up and get the all-clear, you have a 44% reduction in the risk of being diagnosed with CRC for at least four years afterwards,” she told MO.

She added that other data suggest that if patients do have a cancer detected at a screening, it is likely to be at an earlier and more treatable stage, and overall patients will have a lower risk of dying from CRC.

According to Professor Banks, the finding adds more evidence to support changes to the National Bowel Cancer Screening Program (NBCSP) recently announced by the Commonwealth government.

Under the expanded NBCSP, free screening will be offered every two years to Australians between the ages of 50 and 74 by 2020. Seventy-year-olds will be eligible for free screening from 2015 with the remaining age groups between 50 and 74 added each year until 2020.

Med J Aust 2014; 201:523-27