Volumetric Growth Rate of Small Colorectal Polyps on CT Colonography May Be Useful Risk Marker
The growth rates and clinical importance of small colorectal polyps have not been well established. In a study reported in Lancet Oncology, Perry J. Pickhardt, MD, of the University of Wisconsin School of Medicine and Public Health, and colleagues found that volumetric growth rate on computed tomography (CT) colonography can identify proven advanced adenomas and that a minority of small polyps progress over time.
Study Details
In this longitudinal study, asymptomatic adults undergoing routine colorectal cancer screening with CT colonography were enrolled at two U.S. medical centers. Volumes and maximum linear sizes of polyps were measured by CT colonography scans at baseline and surveillance follow-up. Progression was defined as a ≥ 20% volumetric increase per year from baseline and regression was defined as ≥ 20% reduction per year.
Between April 2004 and June 2012, 22,006 asymptomatic adults were screened and 243 adults (mean age 57 years, 37% women) with 306 small colorectal polyps (6–9 mm) were identified. The mean surveillance interval was 2.3 years (range 1–7 years, median 2.0 years). Overall, 68 (22%) of the 306 polyps progressed, 153 (50%) were stable, and 85 (28%) regressed, including apparent resolution in 32 (10%).
Volume Progression and Adenoma Status
Immediate histology was established by colonoscopy for 131 lesions after the final CT colonography. In total, progression occurred in 21 (91%) of 23 proven advanced adenomas, 31 (37%) of 84 proven nonadvanced adenomas, and 15 (8%) of 198 other lesions (P < .0001). The odds ratio for a progressing polyp at CT colonography surveillance to become an advanced adenoma was 15.6 (95% confidence interval [CI] = 7.6–31.7) compared with 6- to 9-mm polyps identified and removed at initial CT colonography screening without surveillance follow-up.
Volume Changes and Absolute Volume
Mean polyp volume changes were a 77% increase per year for 23 proven advanced adenomas, a 16% increase per year for 84 proven nonadvanced adenomas, and a 13% decrease per year for all proven non-neoplastic or unresected polyps (P < .0001). An absolute polyp volume of more than 180 mm3 at surveillance CT colonography identified proven advanced neoplasia with a sensitivity of 92% (22 of 24 polyps, including one delayed cancer), specificity of 94% (266/282), positive predictive value of 58% (22/38), and negative predictive value of 99% (266/268). Only 16 (6%) of the 6- to 9-mm polyps were > 10 mm at follow-up.
The investigators concluded, “Volumetric growth assessment of small colorectal polyps could be a useful biomarker for determination of clinical importance. Advanced adenomas show more rapid growth than nonadvanced adenomas, whereas most other small polyps remain stable or regress. Our findings might allow for less invasive surveillance strategies, reserving polypectomy for lesions that show substantial growth. Further research is needed to provide more information regarding the ultimate fate of unresected small polyps without significant growth.”
The study was funded by the U.S. National Institutes of Health, National Cancer Institute.
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