Special report: New research suggests a type of colon polyp once considered rare may be more common than we think — potentially prompting a change in the way we test for colorectal cancer.

Serrated polyposis syndrome, a condition that increases the risk of a patient developing colorectal (or bowel) cancer, was considered to occur in about 1 in every 3000 people.

But a study between 2015 and 2018 by Port Macquarie gastroenterologist Stuart Kostalas suggests it’s much more common – as many as 3 per cent.

Serrated polyps are a flat, fast growing, precancerous lesion that are difficult to distinguish from other types of polyps in the colon and rectum. They tend to progress to bowel cancer much faster than other types of polyps.

The only way to find out if a polyp is one of these is to remove it via colonoscopy and examine it under a microscope.

Rhythm Biosciences (ASX:RHY) CEO and managing director Dr Trevor Lockett says there is evidence to suggest they are more common in the first third of the colon, the end closest to the small intestine.

“This is a double whammy because in a colonoscopy, it is harder to comprehensively examine the surface near the small intestine for cancerous polyps,” he told Stockhead.

“This could contribute to the reason why cancers in this region – near the small intestine — though less common than in the region of large intestine closer to the rectum, are often proportionately more advanced when discovered.”

New generation screening test could improve diagnosis

There may be ways to help recognise and deal with these higher risk polyps, however.

Currently, the initial screening option for bowel cancer is a stool test — a faecal immune test that looks for blood in the faeces — but many people don’t like taking it.

People at higher risk of bowel cancer go straight to having colonoscopies with which doctors can seek out strange looking polyps and even remove them during the procedure.

But as Dr Lockett says, despite significant advances in colonoscopy imaging technologies, this still isn’t a foolproof method for these types of polyps

“The problem with serrated polyps is that they are often flat,” he said.

“But being flat they can be more difficult to detect visually during colonoscopy.

“Further, during pre-colonoscopy screening these flat serrated polyps are knocked around less by the digesta of the gut as it passes by, leading to a reduced frequency of bleeding relative to the more common hyperplastic polyps.

“This means a lower detection rate by the standard pre-screening test, FIT.”

But if that weren’t enough it’s also often hard to demarcate the borders of these types of polyps. So even if recognised, there is an increased risk of only partial removal of the polyp during the colonoscopic polypectomy procedure.

If the results of the earlier screening test were also able to alert the clinician to any elevated risk of sessile-serrate polyp in a particular patient, forewarned might mean forearmed increasing the likelihood of detection of these important lesions.

Rhythm Biosciences is two years away from commercialising a technology targeted at providing inexpensive blood tests which can more accurately screen patients for colon cancer.

Rather than testing for blood in stool, which can arise for many reasons other than cancer, including from bleeding haemorrhoids or gut inflammation, Rhythm’s ColoSTAT test looks for biomarkers in blood that are produced by the cancer itself.

The company has a major prospective clinical trial planned in early 2019 to assess the ability of ColoSTATTM to detect colorectal cancer.

“There is little doubt that a screening test that can accurately detect these important precancerous lesions of the colon and alert the endoscopist of the added risk could positively impact healthcare outcomes.” Dr Lockett said.

 

This special report is brought to you by Rhythm Biosciences.

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