In a draft recommendation released today, the U.S. Preventive Services Task Force (USPSTF) appears to have thrown CT colonography (CTC) under the bus again, excluding the CT-based exam from its list of recommended colorectal cancer screening tests. The move almost certainly means that Medicare payments will not be forthcoming for CTC.
In its draft recommendation, which is open for public comment until November 2, USPSTF appears to have relied heavily on the same arguments against CTC that the exam's proponents have sought to dispel by accumulating evidence for more than a decade. The recommendation all but dismisses the impact of a raft of new studies commissioned after USPSTF last rejected the exam, in 2008.
In addition to turning down CT colonography, the highly influential semigovernmental group also cast doubt on the value of the Cologuard fecal immunochemical DNA stool test (FIT-DNA).
Dismissed on multiple fronts
According to the draft recommendation, screening with CTC and stool DNA testing may be useful in certain clinical circumstances. However, both of the proposed tests offer "less mature evidence" to support their use, leading to greater uncertainty about their net benefits in even the most appropriate circumstances.
"The USPSTF found no studies that assessed the impact of screening with CT colonography on cancer incidence, morbidity, quality of life, or mortality," the task force wrote. "Although nine studies evaluated the sensitivity and specificity of CT colonography compared with colonoscopy to detect colorectal adenomas, none were designed to determine its diagnostic accuracy to detect colorectal cancer (the overall number of cancer cases in each study was limited)."
The statement is true -- no definitive mortality benefit has been found with CTC -- but the same can be said of conventional colonoscopy. Only fecal occult blood testing has shown a mortality benefit.
Evidence of the optimal screening interval with CTC is also limited, USPSTF wrote. Data modeling suggests that CTC screening of asymptomatic individuals ages 50 to 75 every five years with follow-up for polyps 6 mm and larger could potentially lead to similar benefits as with approved screening tests. But CTC has another problem, USPSTF suggested.
"CT colonography often requires cathartic bowel preparation; this burden is not captured in the primary proxy measure of harms as lifetime number of colonoscopies," USPSTF wrote.
As for extracolonic findings, USPSTF noted that 5% to 37% of extracolonic findings require diagnostic follow-up and about 3% need definitive treatment. Extracolonic findings have the potential to yield both benefits and harms; in terms of harms, they can lead to additional testing and expense, only to find that they posed no harm to the patient's health.
Moreover, radiation-induced cancer remains a potential long-term concern with repeated use of CTC, USPSTF wrote.
"No studies directly measured this risk, but radiation exposure during the procedure appears to be low, with a maximum of about 7 mSv per examination," USPSTF wrote. In comparison, the background level of radiation is 3 mSv per year per person, the group added.
"High-quality evidence remains lacking to draw clear conclusions about the ultimate clinical impact associated with the detection and subsequent workup of extracolonic findings," USPSTF wrote. "Given the frequency with which these incidental findings occur, it is difficult to accurately bound the potential net benefit of this screening test without this information."
Long road to nonapproval
USPSTF rejected the inclusion of CTC as a colorectal cancer screening option once before, in 2008, citing a lack of evidence for its effectiveness in a Medicare-aged screening population. The task force was also concerned about the uncertain effects of radiation, which could potentially be significant if the exam is repeated several times between ages 50 and 75, even though the dose is low.
Following the 2008 rejection, the agency agreed in 2014 to review CTC in light of new evidence showing the procedure's effectiveness in a Medicare population, its lack of significant radiation burden, and the lack of significant harm or expense related to the follow-up of extracolonic findings.
USPSTF's approval is key to securing Medicare reimbursement, because the U.S. Centers for Medicare and Medicaid Services (CMS) is likely to concur with whatever USPSTF recommends, offering the best option for nationwide reimbursement of CTC.
But even before USPSTF's 2008 rejection, CTC has trod a difficult path. The test's most important validation trials took place between 1997 and 2007, revealing sensitivities in the 70% to 95% range.
Then, following the 2008 publication of the American College of Radiology Imaging Network (ACRIN) National CT Colonography Trial, in which CTC demonstrated 92% sensitivity for clinically significant colorectal lesions, the American Cancer Society recommended it as a screening option along with colonoscopy, flexible sigmoidoscopy, the fecal occult blood test, and a barium enema.
Those original recommendations remain largely intact today.
The American College of Radiology is expected to release a statement later today. USPSTF's draft recommendation can be viewed and commented on here.
