Polyp Size and Advanced Histology in Patients Undergoing Colonoscopy Screening: Implications for CT Colonography

Abstract

Background & Aims Colorectal cancer (CRC) screening with diagnostic imaging can detect polyps. The management of patients whose largest polyp is less than 10mm is uncertain. The primary aim of this study was to determine rates of advanced histology in patients undergoing CRC screening whose largest polyp is 9mm or less. Methods Subjects include all asymptomatic adults receiving colonoscopy for screening during 2005 from 17 practice sites, which provide both colonoscopy and pathology reports to the Clinical Outcomes Research Initiative repository. Patients were classified by size of largest polyp. Advanced histology was defined as an adenoma with villous or serrated histology, high-grade dysplasia or an invasive cancer. Risk factors for advanced histology were determined using Pearson chi-square and Fisher’s Exact tests. Results 13,992 asymptomatic patients had screening with colonoscopy; 6360 patients (45%) had polyps, with complete histology available in 5977 (94%). The proportion with advanced histology was 1.7% in the 1–5mm group; 6.6% in the 6–9mm group; 30.6% in the greater than 10mm group; 72.1% in the tumor group. Distal location was associated with advanced histology in the 6–9mm group (p =0.04) and the greater than 10mm group (p = 0.002). Conclusions One in 15 asymptomatic patients whose largest polyp is 6 to 9mm will have advanced histology and would undergo surveillance at 3 years based on current guidelines. Since histology is necessary for this decision, most of these patients should be offered colonoscopy. Further study should determine if patients whose largest polyp is 1–5mm, can be safely followed without polypectomy.

Risk of cancer in small and diminutive colorectal polyps

“…Our results are consistent with much of the previously published literature [3][4][5][6][7][8][9][10][11][12][13][14][15][20][21][22][23][24][25][26][27] , particularly reports from the last 10 years ( Table 2). As noted earlier, the trends toward decreasing prevalence rates of cancer in small and diminutive polyps may reflect the improved imaging capabilities of colonoscopes, and increasing emphasis on identification of flat lesions which do not increase the risk of cancer compared to polypoid lesions [16][17][18] .…”

“…The overall distribution of polyp sizes in this study suggests that the tendency of endoscopists in our unit is to underestimate polyp size, particularly since the percentage of all polyps < 1 cm in size was comparable to other studies [3][4][5][6][7][8][9][10][11][12][13][14][15][21][22][23][24][25][26][27] , despite our center receiving many referrals for large and complex polypectomies 28 . Further the fraction of polyps ≤ 5 mm and 6-9 mm in size was comparable to or higher than prior studies [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][22][23][24][25][26][27][28][29] .…”

“…Further the fraction of polyps ≤ 5 mm and 6-9 mm in size was comparable to or higher than prior studies [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][22][23][24][25][26][27][28][29] . Any underestimation of polyp size would tend to cause the apparent prevalence of cancer in polyps of different size ranges to increase.…”

“…However, more recent colonoscopic studies found a much lower prevalence [8][9][10][11][12][13][14][15] . These differences may reflect in part the improved potential for polyp identification resulting from progressive improvements in colonoscope imaging.…”

CTC Interpretation by Gastroenterologists

“…To put this into clinical context, assuming a 14 % screening prevalence of non-diminutive polyps (3) and a 90 % detection sensitivity (which was achieved by only one of seven readers), a 70 % specifi city will result in twice as many false-positives as true-positives. If all CTC-detected lesions ≥ 6 mm were sent for polypectomy, which many gastroenterologists advocate (4,5) , then a large number of additional costly and invasive procedures would be unnecessarily performed. If CTC specifi city falls below 70 % , or the polyp prevalence decreases, the positive predictive value plummets even further.…”