CT Colonography Gets Another Look

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 - Colon

As colorectal cancer screening research marches on and options for screening continue to be evaluated, one constant remains: CT colonography is not covered by Medicare. However, some private payers cover the screening exam and this year it’s getting another look at the federal level. Where does CT colonography currently stand in the colorectal screening landscape?

This past summer, when the Centers for Medicare & Medicaid Services (CMS) approved Medicare coverage of a stool DNA colorectal cancer screening test, many in the imaging community were left wondering, “What about CT colonography?”

The DNA screening test was granted coverage under a new joint approval process with the FDA, but the American College of Radiology (ACR) drafted a letter to CMS arguing that CT colonography’s performance exceeds the standard applied to the DNA test.

“That [approval process] had not been available previously for CT colonography and it’s only for new techniques, so CT colonography is not eligible for that same route,” says Judy Yee, MD, chair of ACR’s Colon Cancer Committee and chief of radiology at the San Francisco VA Medical Center. Yee was the signed author of ACR’s letter to CMS.

One of the disappointing facets of seeing the DNA test approved in a joint process with the FDA is that CT colonography was already reviewed by the FDA in fall 2013. Yee notes that there was unanimous approval from the FDA Gastroenterology-Urology Devices Panel that CT colonography is safe and effective.

Approval of the DNA test while CT colonography remains in Medicare coverage limbo is just the latest chapter in the years’ long debate over whether Medicare beneficiaries should have the screening test covered. CIGNA, Anthem Blue Cross Blue Shield and a number of other payers currently cover screening CT colonography, but Medicare does not, and that could have a big impact on who is getting screened. While studies have shown that patients prefer CT colonography and would be more likely to go through with screening if it were an option (Am J Roentgenol. 2012 Jun;198:1361-6), most are not willing to pay out-of-pocket if insurance didn’t pick up the tab (Am J Roentgenol. 2010 Aug;195:393-7).

Multiple screening options, different purposes

Colorectal cancer screening guidelines from the American Cancer Society and ACR divide screening tools into two broad categories: those meant to identify cancer and those meant to prevent cancer.

The stool DNA test falls into the former group along with fecal immunochemical tests or the fecal occult blood test. These screening tools are not meant to prevent cancer, but instead are used to see whether a patient has it or not. “The intent of the stool DNA test is really to identify the cancer. It’s almost too late by then,” says Yee.

CT colonography, on the other hand, has high sensitivity for identifying precursor lesions that can be removed in order to prevent cancers. Other screening options that can help prevent cancer include colonoscopy and flexible sigmoidoscopy.

Perry Pickhardt, MD, professor in the Department of Radiology at the University of Wisconsin School of Medicine and Public Health, is a proponent of CT colonography and points out that not only is CT colonography more sensitive and specific for cancer than stool DNA, but it also can detect greater than 90 percent of advanced adenomas versus around 40 percent detection by stool DNA. He thinks any lingering concerns regarding CT colonography have already been answered. “CT colonography is clearly a good colorectal cancer screening test – perhaps the best of the available options. It is accurate, safe, fast, and convenient for patients.”

When asked what factors, then, are hindering more widespread adoption of CT colonography screening, Pickhardt says it’s mostly a lack of awareness, primarily among primary care providers. “Primary care physicians are largely late adopters of new technology.” He adds that the perceived “turf battle” with gastrointestinal specialists is another negative factor that can interfere with improved patient care and cost-effectiveness.

The endoscopic preventative screening methods do have their own advantages. Colonoscopy can save patients from having to go through multiple unpleasant bowel preparations since polyps can be removed during the initial exam if colonoscopy is used as the primary screening method. Large polyps discovered on CT colonography will often require a second procedure.

A recent Norwegian study of screening with one-time flexible sigmoidoscopy also touted the effectiveness of that technique. The study, published in the August 13 issue of JAMA by Øyvind Holme, MD, and colleagues, of the Sorlandet Hospital Kristiansand in Kristiansan, Norway, featured nearly 100,000 participants and found flexible sigmoidoscopy dropped the colorectal cancer incidence rate by 20 percent and the death rate by 27 percent.

That same study also looked at the effect of adding fecal occult blood testing to screening with flexible sigmoidoscopy and found it did not make a difference in outcomes.

In an associated editorial on the Norwegian study, Allan S. Brett, MD, professor of clinical internal medicine at the University of South Carolina School of Medicine, wrote that the study highlights an irony for U.S. clinicians in that colonoscopy has become the most common endoscopic colorectal cancer screening tool while sigmoidoscopy has nearly vanished.

Despite the muddled landscape of colorectal cancer screening in the U.S., Brett is bullish on the prospects of stool DNA testing, saying it has the potential to reduce colorectal cancer mortality while at the same time cutting the number of routine colonoscopies.

“A screening strategy in which everyone gets colonoscopy ultimately exposes many people to an inconvenient, expensive, and moderately invasive procedure in order to benefit a relatively small proportion of the population, Brett told Health Imaging. “Any less-invasive testing strategy that could limit the number of colonoscopies should be a welcome advance in screening, as long as it preserves a reduction in colorectal cancer mortality that is similar to a ‘colonoscopy-for-all’ approach.”

USPSTF review redux

So where does all this leave proponents of CT colonography? In the familiar position of waiting for the U.S. Preventive Services Task Force (USPSTF) to weigh in. In a 2008 review of CT colonography, the USPSTF gave the screening exam an “I” rating for insufficient evidence. Earlier this year, however, the task force included CT colonography in a draft research plan for colorectal cancer screening, setting the stage for potential Medicare reimbursement in the future.

Yee says it’s not a guarantee, but other options become available, such as coverage with evidence development, once the procedure moves out of the I rating. “If USPSTF were to come out with an A or B rating, then there would be interest on the part of CMS to look at reimbursing screening CT colonography nationally.”

An outcome of the USPSTF review is expected at the end of 2014 or early 2015.

CT Colonography Effectively Identifies Carpet Lesions
A retrospective review of more than 9,000 adults undergoing initial CT colonography, published in the February issue of Radiology, demonstrated the exam was able to effectively depict neoplastic carpet lesions. While carpet lesions, a subset of nonpolypoid colorectal lesions, are rare, they have demonstrated clinical relevance, so Perry J. Pickhardt, MD, of the University of Wisconsin in Madison, and colleagues aimed to describe the clinical, imaging, and pathologic features of carpet lesions at CT colonography. The average width and height of such lesions was 46.5 mm and 7.9 mm, respectively, and the majority were spotted in the distal rectosigmoid or proximal right colon. Computer-aided detection hits caught 94.4 percent of the lesions. “There is a common misperception that CT colonography cannot detect flat lesions, but we actually do quite well,” says Pickhardt.

Images show cecal carpet lesion detected at screening CT colonography in 50-year-old man; blue regions with arrows identify focal areas of a 3.5-cm carpet lesion.

Source: (Radiology 2014;270:435-443)