Figures from a Victorian familial bowel cancer service support more intensive screening for first degree relatives of people with colorectal cancer.

The prevalence rates for adenomas, advanced adenomas, and colorectal cancer in people with two parents affected by colorectal cancer are higher than those seen in average-risk populations, according to Victorian researchers.

However prior to 2017, guidelines did not treat people with a first-degree relative from different sides of their families as if they had an elevated risk of CRC.

A study from the Familial Bowel Cancer Service at the Royal Melbourne Hospital comprised 96 individuals from 62 families who were registered with the surveillance database between 1980 and 2015.

Registrants began screening as early as 24 years of age and as late as 70 years of age, with the mean age of first screening at about 45 years.

During the study period, registrants typically underwent over 11 FOBTs and 4 colonoscopies.

The study found prevalence rates of adenomas (40.6 v 30.2%), advanced adenomas (10.4 v 5.7%) and CRC (6.9 v 0.3%) were higher on the basis on colonoscopy findings than in an average-risk North American population.

The mean age of a first neoplastic finding was 53.5 years with over half (53.7%) found before 55 years of age.

The ages of the parents at CRC diagnosis did not appear to impact the presence of neoplasms or advanced neoplasms in registrants.

However registrants with an advanced neoplasm were more likely to also have a sibling with an advanced neoplasm.

The study found that out of all colonoscopies in which neoplasms were identified only 14.8% had an FOBT that was positive within the previous six months.

“This further suggests that many of these registrants with neoplasms would have been missed under the average-risk individual categorisation and with use of FOBT alone for screening,” the study said.

Senior author Professor Finlay Macrae told the limbic the study provided support for the more intensive screening for this subpopulation now applied in the current guidelines.

He said the 2017 guidelines were based on evidence from an American registry study that had now been validated in an Australian context.

“This study is taking it a step further in actually checking them with colonoscopy and finding that, indeed, they were at higher risk,” he said.

“Not everyone has caught up with the change that both sides of the family can now be counted into that moderate risk category. It’s not well known. It’s a subtle change but a definite change and this study supports that.”