In a new model analysis published Tuesday in the Journal of the National Cancer Institute, virtual colonoscopy was generally less cost-effective than several other colon cancer screening tests, including conventional colonoscopy. However, VC would become the most cost-effective test if it were to increase colon cancer screening rates.
To arrive at their conclusions, the authors used three analytic models developed independently in the wake of the U.S. Centers for Medicare and Medicaid Services' (CMS) 2008 denial of coverage for virtual colonoscopy (J Natl Cancer Inst, July 27, 2010).
An editorial accompanying the article by cancer expert Russell Harris, MD, from the University of North Carolina at Chapel Hill, said that given the inadequacy of existing data at key points, judgment is required to fill in the gaps and make a decision about screening with virtual colonoscopy (also known as CT colonography or CTC). And considering the rift between gastroenterologists and radiologists on this issue, those evidence gaps make agreement unlikely on this issue.
Indeed, Perry Pickhardt, MD, a radiologist from the University of Wisconsin in Madison who was not involved in the research, said the study actually supports the conclusion that CTC would be cost-effective, inasmuch as emerging data show that substantially more patients would be screened if CTC were available.
Study follows coverage denial
Principal investigator Amy Knudsen, PhD, from Massachusetts General Hospital in Boston, said the study grew out of analysis methods used for the CMS analysis and eventual denial of CTC coverage in 2008. The use of CTC was considered for coverage because it may be more acceptable to patients than conventional colonoscopy.
"Recent studies have demonstrated that CTC and colonoscopy have similar sensitivities for detection of adenomas 10 mm or larger," Knudsen and her colleagues wrote. "Because CTC is less invasive than colonoscopy, it may be more acceptable to patients. However, patients undergoing CTC must undergo extensive bowel preparation similar to that required for colonoscopy, and suspicious lesions identified on CTC require the patient to undergo a second procedure (colonoscopy) for biopsy or removal."
The authors sought to evaluate the reimbursement rate at which CTC screening would be cost-effective compared with currently reimbursed colorectal cancer screening tests, including annual fecal occult blood test (FOBT), flexible sigmoidoscopy every five years, flexible sigmoidoscopy every five years in conjunction with annual FOBT, and colonoscopy every 10 years.
Three independently developed microsimulation models were used to assess the health outcomes and costs associated with VC screening and the other tests in the average-risk Medicare population:
- The Microsimulation Screening Analysis (MISCAN) model from Erasmus University Medical Center (Rotterdam, Netherlands) and Memorial Sloan-Kettering Cancer Center (New York City)
- The Simulation Model of Colorectal Cancer (SimCRC) from the University of Minnesota (Minneapolis) and Massachusetts General Hospital (Boston)
- The Colorectal Cancer Simulated Population Model for Incidence and Natural History (CRC-SPIN) from the Group Health Research Institute (Seattle)
Virtual colonoscopy was assumed to be performed every five years, using sensitivity data from the 2003 U.S. Department of Defense study or the 2008 ACRIN 6664 trial.
All three models simulate the life histories of a large population of individuals from birth to death, adding a natural history component that tracks colorectal disease progression in patients who are not screened, the authors explained. As the modeled individual ages, one or more adenomas may develop, and the risk of developing an adenoma depends on the individual's age, sex, and individual risk. Based on the literature, some grow and become malignant.
"A preclinical (i.e., undetected) cancer has a chance of progressing from stage I to stage IV and may be detected by symptoms at any stage," Knudsen and colleagues wrote.
The study team calculated incremental cost-effectiveness ratios for the reimbursed screening tests, and the maximum cost per scan (threshold) for the CTC strategy to achieve efficiency compared to the other tests, performing sensitivity analyses on the key parameters and assumptions.
Costs for reimbursed tests (i.e., everything but CTC) were based on 2007 average Medicare payments, as were the costs and frequency of polypectomy, which included weighted averages of associated services including sedation.
For CTC, the authors used CMS payments for abdominal and pelvic CT, plus a charge for image processing. They modeled risks including colonic perforation, weighted higher in colonoscopy, which was also associated with serosal burns and bleeding that might require transfusion.
Increasing life years
All of the tests succeeded in significantly increasing expected life years. Assuming that patients adhered 100% to all screening guidelines, the use of CTC delivered undiscounted life-year gains ranging from 143 to 178 per 1,000 65-year-olds in the three models, slightly less than the number of life years gained from colonoscopy every 10 years (152-185 life years per 1,000 65-year-olds) and comparable to life-year gains from flexible sigmoidoscopy every five years along with an annual FOBT test (149-177 life years per 1,000 65-year-olds), the authors reported.
In the SimCRC and CRC-SPIN models, colonoscopy every 10 years was the most effective strategy for producing life-year gains (171 and 185 additional life years, respectively), the authors wrote. In the MISCAN model, the combination of flexible sigmoidoscopy with annual FOBT (hemoccult SENSA or immunochemical FOBT) was the most effective strategy, saving 154 life years per 1,000 65-year-olds versus no screening. Colonoscopy once per decade saved 152 life years per 1,000 65-year-olds screened.
CTC costs versus other options
"If CTC screening was reimbursed at $488 per scan (slightly less than the reimbursement for a colonoscopy without polypectomy), it would be the most costly strategy," the authors wrote. At current screening rates, virtual colonoscopy would be cost-effective only at $108-$205 per scan, depending on the microsimulation model used.
However, if colorectal cancer screening rates were to increase due to the availability of CTC, it could be the most cost-effective test at much higher reimbursement rates, they wrote.
"If individuals who would not be screened otherwise would agree to be screened with CTC, the threshold costs would increase compared with the base-case estimates," Knudsen and colleagues reported. "With 10% of otherwise unscreened individuals adopting CTC screening (i.e., an increase in overall adherence from 57% to 62.7%), CTC screening became the most effective strategy and threshold costs ranged from $204 to $408. ... With 25% of otherwise unscreened persons adopting CTC screening (i.e., an increase in overall adherence from 57% to 71.3%), the threshold costs ranged from $433 to $694."
In any case, they added, CTC's cost per incremental life year was well within generally accepted cost thresholds for life-year gains. Although CTC screening at $488 was dominated by at least one of the other screening options, "the incremental cost per discounted life year gained of CTC compared with no screening was less than $10,000 in all three models and for each set of CTC test characteristics and ranged from $1,800 to $9,500," they wrote.
Reducing CTC referrals to colonoscopy and reducing the sensitivity of optical colonoscopy also reduced the cost-effectiveness threshold for VC, the group wrote.
"In all three models, restricting follow-up colonoscopy to individuals with CTC findings of 10 mm or larger lowered threshold costs for CTC compared with the threshold costs from the base-case analysis," Knudsen and her team wrote. "Decreasing the specificity of colonoscopy from 90% to 80% by assuming that one or more nonadenomatous polyps was removed for biopsy in 20% of colonoscopies modestly increased the threshold costs for CTC."
Assuming perfect adherence, the life-year gains for CTC and colonoscopy were similar for all three models, with only a slight advantage for colonoscopy, the group concluded. From a cost standpoint, however, the need to perform VC every five years rather than every 10 for conventional colonoscopy puts it at a disadvantage relative to colonoscopy.
"Thus, even for people who never have an abnormality detected, the costs of CTC are incurred twice as frequently as the cost of colonoscopy, whereas those who have a positive finding on CTC accrue the cost of a diagnostic colonoscopy in addition to the cost of the screening CTC," they wrote.
Considering that a rise in screening compliance would increase the threshold amount that could be charged for CTC, "research on techniques to improve detection rates with CTC may be less important in informing future coverage decisions than studies that assess whether or not individuals who have yet to be screened for colorectal cancer deem CTC more acceptable than other colorectal cancer screening options."
But the authors said they were unaware of any study that evaluated whether adding VC to the menu of screening options increases adherence among individuals who were previously unwilling to be screened.
Therefore, if CTC is reimbursed at roughly the same rate as colonoscopy, the cost relative to the benefits and availability of other tests is too high for it to be a cost-effective screening strategy, the study team concluded. But lower costs of CTC, or a significant increase in compliance resulting from its availability, would make it so.
Comments
In a letter to the journal editor that was also provided to AuntMinnie.com for this story, the University of Wisconsin's Pickhardt said that he disagreed with some of the assumptions used in the article (particularly regarding the natural history of polyps), but that the key issues in the study were cost and compliance, on which he largely agreed with the authors.
Knudsen and colleagues used a threshold cost percentage for CTC relative to colonoscopy, comparing that value to previous analyses that generally found CTC to cost between 40% and 80% of other studies. "At our institution, the charge for colonoscopy is three to five times that for CTC, which fits well within this threshold," Pickhardt wrote.
However, he said, data show that higher compliance rates are likely to result from the availability of CTC.
"Survey data from the largest CTC screening experience in the U.S. indicate that nearly 40% of individuals screened by CTC would have foregone screening if CTC had not been an available option" (Moawad et al, 2010, American Journal of Roentgenology, in press), Pickhardt wrote. Another new study, by Ho et al (AJR, August 2010, Vol. 195:2, pp. 393-397), found that more than 80% of a nonadherent urban cohort said they would be willing to undergo CTC.
"These findings are all of particular relevance to the Medicare population, where a large study found that overall adherence rates were less than 30%, making the goal of a 25% CTC-related increase appear to be a relatively soft target," Pickhardt wrote. "Given the central importance of adherence rates to cost-effectiveness for colorectal cancer screening, it appears such evidence may be the 'missing link' needed to put CTC over the top."
In his editorial accompanying the study, the University of North Carolina's Harris said the many uncertainties surrounding any analysis of the comparative costs and benefits show the difficulty of arriving at firm conclusions. One example is the uncertainty about the natural history of diminutive polyps, and the most effective screening strategy.
"If these small polyps are an important cause of colorectal cancer mortality, and waiting until the next screening round is not effective in preventing these deaths, then optical colonoscopy would provide more benefit than CT colonography," Harris wrote. "But if these polyps are not important contributors to colorectal cancer mortality, or if waiting until the next screening round is as effective as detecting them when they are small, then polyps are being removed unnecessarily by optical colonoscopy -- a form of 'overtreatment' -- subjecting many people to an increased risk of optical colonoscopy complications and subjecting all of us to increased cost."
The microsimulation models accounted for the costs of the potentially unnecessary polypectomies, but they were unable to quantify the effect of their complications on quality of life, he wrote. Similarly, dealing with extracolonic findings could potentially increase the costs and risks of CTC, while low sensitivity for right-sided cancers works against the effectiveness of conventional colonoscopy. Nevertheless, "carefully performed" studies such as these represent a valuable contribution to the debate, he wrote.
"Perhaps neither gastroenterologists nor radiologists are unbiased enough to speak for this evidence," Harris wrote. "There are important uncertainties, and even with modeling and our best guesses, the trade-offs between benefits and harms are not obvious."
By Eric Barnes
AuntMinnie.com staff writer
July 27, 2010
Related Reading
Virtual colonoscopy adds to number of people getting screened, May 17, 2010
5-year C-RADS analysis shows stable VC screening results, May 6, 2010
Editorial: CMS unfairly held VC to higher standard, February 5, 2010
JACR editorial: Medicare used double standard in VC decision, September 22, 2009
NEJM editorial lauds CMS rejection of VC, May 28, 2009
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