Clinical Management of Small Polyps Detected at Screening CT Colonography
Clinical Management of Small Polyps Detected at Screening CT Colonography
Objective. The primary aim of this model analysis was to compare the clinical and economic impacts of immediate polypectomy versus 3-year CT colonography (CTC) surveillance for small (6- to 9-mm) polyps detected at CTC scre ening.
Materials and Methods. A decision analysis model was constructed incorporating the expected advanced neoplasia prevalence, frequency of measurable growth, colorectal cancer (CRC) prevalence and risk, CTC performance, and costs related to CRC screening and treatment. CRC risk was assumed to be independent of advanced adenoma size, which intentionally overestimates the risk related to small polyps. Clinical effectiveness and costs for 3-year CTC surveillance versus immediate colonoscopic polypectomy were compared for a concentrated cohort of patients with 6- to 9-mm polyps. For the CTC surveillance strategy, only cases with measurable growth (≥ 1 mm) at follow-up CTC were referred fo r polypectomy.
Results. Without any intervention, the estimated 5-year CRC death rate from 6- to 9-mm polyps in this concentrated cohort was 0.08%, which is a sevenfold decrease over the 0.56% CRC risk for the general unselected screening population. The death rate was further reduced to 0.03% with the CTC surveillance strategy and to 0.02% with immediate colonoscopy referral. However, for each additional cancer-related death prevented with immediate polypectomy versus CTC follow-up, 9,977 colonoscopy referrals would be needed, resulting in 10 additional perforations and an incremental cost-effectiveness ratio of $37 2,853.
Conclusion. For patients with small (6- to 9-mm) polyps detected at CTC screening, the exclusion of large polyps (≥ 10 mm) already confers a very low risk of CRC. The high costs, additional complications, and relatively low incremental yield associated with immediate polypectomy of 6- to 9-mm polyps support the practice of 3-year CTC surveillance, which allows for selective noninvasive identificati on of small polyps at risk.
Colorectal cancer (CRC) is a major cause of morbidity and mortality in Western societies, and its thera peutic costs are a substantial economic burden. According to the widely accepted adenoma-to-carcinoma sequence, most cancers develop from a small subset of benign adenomatous polyps with a long dwell time. Therefore, colorectal screening of average-risk adults based on polyp detection and cancer prevention is widely accepted. The overall efficacy of a screening program depends on a number of factors, including sensitive detection of clinically meaningful lesions, available resources, insurance coverage, and patient compliance. Optical colonoscopy is accurate in identifying colorectal neoplasia, but patient compliance with colonoscopy screening has been disappointingly low compared with other programs such as breast cancer screening.
Noninvasive strategies exploiting recent technologic advances may substantially improve the compliance rate without af fecting the sensitivity for detecting clinically relevant lesions. Among these emerging screening options, CT colonography (CTC) has shown excellent performance characteristics for the detection of advanced neoplasia when current techniques are applied. In fact, the recently revised colorectal screening guidelines of the American Cancer Society now include CTC as a recommended screening test, emphasizing its ability for prevention. CTC offers the potential for selectively and noninvasively filtering out those patients who would benefit most from therapeutic colonoscopy.
Colonoscopic referral for diminutive polyps (≤ 5 mm) detected at CTC has been shown to be a highly ineffective approach because of the extremely low likelihood of advanced neoplasia and the high costs associated with polypectomy. In comparison, the clinical management of small (6- to 9-mm) polyps detected at CTC remains controversial, in part because of the perceived lack of data regarding the natural history of these lesions. Although the current clinical practice is generally to offer polypectomy for small (6- to 9-mm) polyps detected at CTC, many patients will choose short-term CTC surveillance if presented with the option. To date, no detrimental effect has been shown from longitudinal follow-up of small colorectal polyps in previous endoscopic and barium enema studies, suggesting that this may be a reasonable clinical approach. In fact, most small polyps will either remain stable or decrease in size over time, which agrees with our preliminary experience with CTC surveillance of 6- to 9-mm polyps.
A previous decision analysis predicted an unexpectedly high rate of cancers resulting from short-term CTC follow-up of 6- to 9-mm polyps. However, that analysis was largely based on data from high-risk or symptomatic cohorts and lacked appropriate natural history assumptions based on actual CTC observational surveillance studies. In addition, no cost-effectiveness analysis was performed, precluding evaluation of the cost efficiency for referring patients from CTC to colonoscopy.
To address the previous shortcomings in the knowledge of the natural history of small polyps, we recently developed a model in which the distribution of advanced neoplasia according to polyp size was projected on the CRC risk for the general population. In addition, we now have initial input data from longitudinal CTC surveillance of 6- to 9-mm polyps that show that only a small percentage of small polyps, including the expected number of histologically advanced lesions, will show measurable interval growth (Pickhardt PJ et al., presented at the 2008 meeting of the Society of Gastrointestinal Radiologists). This observation should allow noninvasive distinction from stable lesions without concerning histologic features. It is highly unlikely that a nonadvanced subcentimeter tubular adenoma will progress to cancer over 5–10 years; most cancers will likely arise from progression of adenomas that are already histologically advanced. To date, no assessment has been made of the cost-effectiveness of short-term CTC surveillance for small polyps, as currently recommended by radiology consensus guidelines. The aim of this decision analysis was to compare the relative benefits, harms, costs, and resource utilization of short-term CTC surveillance for 6- to 9-mm lesions detected at CTC screening, compared with a policy of immediate colonoscopic referral for polypectomy.
Abstract and Introduction
Abstract
Objective. The primary aim of this model analysis was to compare the clinical and economic impacts of immediate polypectomy versus 3-year CT colonography (CTC) surveillance for small (6- to 9-mm) polyps detected at CTC scre ening.
Materials and Methods. A decision analysis model was constructed incorporating the expected advanced neoplasia prevalence, frequency of measurable growth, colorectal cancer (CRC) prevalence and risk, CTC performance, and costs related to CRC screening and treatment. CRC risk was assumed to be independent of advanced adenoma size, which intentionally overestimates the risk related to small polyps. Clinical effectiveness and costs for 3-year CTC surveillance versus immediate colonoscopic polypectomy were compared for a concentrated cohort of patients with 6- to 9-mm polyps. For the CTC surveillance strategy, only cases with measurable growth (≥ 1 mm) at follow-up CTC were referred fo r polypectomy.
Results. Without any intervention, the estimated 5-year CRC death rate from 6- to 9-mm polyps in this concentrated cohort was 0.08%, which is a sevenfold decrease over the 0.56% CRC risk for the general unselected screening population. The death rate was further reduced to 0.03% with the CTC surveillance strategy and to 0.02% with immediate colonoscopy referral. However, for each additional cancer-related death prevented with immediate polypectomy versus CTC follow-up, 9,977 colonoscopy referrals would be needed, resulting in 10 additional perforations and an incremental cost-effectiveness ratio of $37 2,853.
Conclusion. For patients with small (6- to 9-mm) polyps detected at CTC screening, the exclusion of large polyps (≥ 10 mm) already confers a very low risk of CRC. The high costs, additional complications, and relatively low incremental yield associated with immediate polypectomy of 6- to 9-mm polyps support the practice of 3-year CTC surveillance, which allows for selective noninvasive identificati on of small polyps at risk.
Introduction
Colorectal cancer (CRC) is a major cause of morbidity and mortality in Western societies, and its thera peutic costs are a substantial economic burden. According to the widely accepted adenoma-to-carcinoma sequence, most cancers develop from a small subset of benign adenomatous polyps with a long dwell time. Therefore, colorectal screening of average-risk adults based on polyp detection and cancer prevention is widely accepted. The overall efficacy of a screening program depends on a number of factors, including sensitive detection of clinically meaningful lesions, available resources, insurance coverage, and patient compliance. Optical colonoscopy is accurate in identifying colorectal neoplasia, but patient compliance with colonoscopy screening has been disappointingly low compared with other programs such as breast cancer screening.
Noninvasive strategies exploiting recent technologic advances may substantially improve the compliance rate without af fecting the sensitivity for detecting clinically relevant lesions. Among these emerging screening options, CT colonography (CTC) has shown excellent performance characteristics for the detection of advanced neoplasia when current techniques are applied. In fact, the recently revised colorectal screening guidelines of the American Cancer Society now include CTC as a recommended screening test, emphasizing its ability for prevention. CTC offers the potential for selectively and noninvasively filtering out those patients who would benefit most from therapeutic colonoscopy.
Colonoscopic referral for diminutive polyps (≤ 5 mm) detected at CTC has been shown to be a highly ineffective approach because of the extremely low likelihood of advanced neoplasia and the high costs associated with polypectomy. In comparison, the clinical management of small (6- to 9-mm) polyps detected at CTC remains controversial, in part because of the perceived lack of data regarding the natural history of these lesions. Although the current clinical practice is generally to offer polypectomy for small (6- to 9-mm) polyps detected at CTC, many patients will choose short-term CTC surveillance if presented with the option. To date, no detrimental effect has been shown from longitudinal follow-up of small colorectal polyps in previous endoscopic and barium enema studies, suggesting that this may be a reasonable clinical approach. In fact, most small polyps will either remain stable or decrease in size over time, which agrees with our preliminary experience with CTC surveillance of 6- to 9-mm polyps.
A previous decision analysis predicted an unexpectedly high rate of cancers resulting from short-term CTC follow-up of 6- to 9-mm polyps. However, that analysis was largely based on data from high-risk or symptomatic cohorts and lacked appropriate natural history assumptions based on actual CTC observational surveillance studies. In addition, no cost-effectiveness analysis was performed, precluding evaluation of the cost efficiency for referring patients from CTC to colonoscopy.
To address the previous shortcomings in the knowledge of the natural history of small polyps, we recently developed a model in which the distribution of advanced neoplasia according to polyp size was projected on the CRC risk for the general population. In addition, we now have initial input data from longitudinal CTC surveillance of 6- to 9-mm polyps that show that only a small percentage of small polyps, including the expected number of histologically advanced lesions, will show measurable interval growth (Pickhardt PJ et al., presented at the 2008 meeting of the Society of Gastrointestinal Radiologists). This observation should allow noninvasive distinction from stable lesions without concerning histologic features. It is highly unlikely that a nonadvanced subcentimeter tubular adenoma will progress to cancer over 5–10 years; most cancers will likely arise from progression of adenomas that are already histologically advanced. To date, no assessment has been made of the cost-effectiveness of short-term CTC surveillance for small polyps, as currently recommended by radiology consensus guidelines. The aim of this decision analysis was to compare the relative benefits, harms, costs, and resource utilization of short-term CTC surveillance for 6- to 9-mm lesions detected at CTC screening, compared with a policy of immediate colonoscopic referral for polypectomy.