medwireNews: Monitoring colorectal polyp growth with computed tomography (CT) could help target treatment in patients undergoing routine colorectal cancer surveillance, research suggests.
CT results show that advanced adenomas - defined as a polyp with a prominent villous component, high-grade dysplasia, invasive cancer on histology, or a lesion of at least 10 mm in size - were significantly more likely to grow between screening than non-advanced adenomas, while other small polyps were likely to remain the same size or shrink over time.
"These findings could allow for less invasive surveillance strategies of small colorectal polyps, reserving polypectomy for lesions that show substantial growth," say Perry Pickhardt (University of Wisconsin School of Medicine and Public Health, Madison, USA) and co-authors in The Lancet Oncology.
The study included data for 243 patients, aged an average of 57.4 years, with 306 small polyps between 6 and 9 mm in diameter detected during routine CT colorectal cancer screening.
The patients underwent repeat CT an average of 2.3 years later, at which point 22% of polyps had progressed from baseline (>20% increase in volume per year), 50% were stable (within 20% growth or shrinkage), and 28% had regressed or resolved (>20% reduction in volume).
Histology of 131 lesions removed at the final CT showed that 91% of 23 proven advanced adenomas had progressed during the surveillance interval, compared with just 37% of 84 non-advanced adenomas and 8% of 198 other lesions, a significant difference.
Indeed, on average, there was a 77% increase in polyp volume per year for proven advanced adenomas, whereas proven non-advanced adenomas had a 16% increase per year and proven non-neoplastic or unresected polyps had a 13% decrease in volume per year.
Using a polyp cutoff for absolute volume above 180 mm3 at surveillance CT colonography, the researchers were able to identify proven advanced neoplasia with 92% sensitivity and 94% specificity.
Just 6% of the 6-9 mm polyps were greater than 10 mm in diameter at follow up.
Noting that a polyp that progressed in the surveillance interval was 15.6 times more likely to become an advanced adenoma than a polyp removed at the initial colonograph screening in a comparison patient cohort, the researchers conclude: "Volumetric growth of colorectal polyps seems to be a powerful biomarker, which can concentrate the lesions of clinical significance, potentially leaving behind most unimportant lesions."
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