Volumetric growth may provide CT colonography biomarker

Volumetric growth may help determine the clinical significance of small polyps detected at CT colonography, according to a study published in the July issue of The Lancet.

Small colorectal polyps (6-9 mm) present a clinical conundrum in CT colonography screening. Large polyps (≥ 10 mm) are managed more aggressively, and polyps ≤ 5 mm are treated as benign. Management of small polyps represents an uncertain middle ground, “for which treatment decisions are contentious [and] could have an enormous effect on colorectal cancer screening, irrespective of modality,” wrote Perry J. Pickhardt, MD, from the University of Wisconsin School of Medicine and Public Health in Madison, and colleagues.

Pickhardt and colleagues sought to evaluate the behaviors of 6-9 mm polyps with CT colonography assessments to determine whether growth rates were predictive of neoplasia, advanced adenomas and clinical importance. The researchers screened 22,006 asymptomatic adults between April 2004 and June 2012 and focused on 243 individuals with 306 small colorectal polyps.

Polyp growth was categorized as progression, stability or regression via measured changes at follow-up CT colonographies. The researchers used a 20 percent per year threshold to determine baseline categorization.

During the mean surveillance interval of 2.3 years, 68 polyps progressed, 153 were stable and 85 regressed. “Polypectomy was indicated for all lesions showing linear growth of 1 mm or more at interval CT colonography.”

Histological changes were reported following resection for 131 polyps. A total 21 of 23 proven advanced adenomas progressed, compared with 31 of 84 proven non-advanced adenomas and 15 of 198 other lesions. “Ongoing surveillance of unresected small polyps that did not show substantial growth to date at follow-up CT colonographies might help explain what ultimately happens to these less aggressive lesions.”

The study demonstrated the strong link between volumetric growth and clinical relevance, according to Pickhardt et al. “Volumetric growth of colorectal polyps seems to be a powerful biomarker, which can concentrate the lesions of clinical significance, potentially leaving behind most important lesions,” they wrote.

The researchers pointed to another advantage of CT colonography over other surveillance modalities: It can precisely and retrospectively define and measure polyps over multiple exams.

Finally, the findings support current recommendations that call for polypectomy referral or three-year CT colonography surveillance for patients with one or two small polyps detected at CT colonography.