Diagnostics & Imaging Week National Editor
A just-released study comparing standard colonoscopy with the somewhat less-invasive, and less-uncomfortable computer tomographic (CT) colonography (CTC, also termed "virtual" colonoscopy) concludes that the two are equally effective in assessing, and possibly heading off, early colon cancer.
The study, appearing in this week's issue of the New England Journal of Medicine, serves to ratchet up a turf war in the human gut – not a pretty sight (or site) but one whose outcome could spell life or death for those who decide to get, and too often not get, an assessment for colorectal cancer.
The first report of that study and its conclusion immediately drew a statement from the American College of Gastroenterology (ACG; Philadelphia), a major advocate of the standard procedure, providing a variety of comments qualifying those conclusions. The ACG raised what it called "several important issues" concerning the virtual procedure.
The study of 2,600 patients at 15 centers in the U.S. — the National CT Colonography Trial, conducted by the American College of Radiology Imaging Network (ACRIN; Bethesda, Maryland) and supported by the National Institutes of Cancer of the NIH – compared the two procedures and concludes that CTC has an equal ability to identify small polyps that are precancerous. And ACRIN said in a statement that the method "could serve as an initial screening exam" to detect colorectal cancer.
ACRIN describes CTC as employing "virtual reality technology" to create 3-D images that provide "a thorough and minimally invasive" assessment of the colon and rectum." And its principle investigator said that CTC "could be adopted into the mainstream of clinical practice as a primary option for colorectal cancer screening."
The study's primary focus was the identification of polyps 10 mm or larger, with CTC highly accurate in finding this.
A trial Q&A says that polyps of this size are the most likely to become cancerous. It adds: "However, smaller polyps can also become cancerous, and this study demonstrated that CTC is able to detect polyps as small as 5 mm in width (about the diameter of a pencil) with high sensitivity."
In a statement, the ACG challenged the value of these findings. Its president, Amy Fox-Orenstein, DO, asserting that a CTC does not rule out the need for follow-on standard colonoscopy, and that "the reality [is] that many patients who have polyps detected by CT colonography will still have to undergo complete colonoscopy," though less than 17% of study participants, perhaps up to 30% in real-world circumstances.
She added: "Of more significant concern, is that the researchers only reported growths in the colon [of] 5 mm or larger, leaving unreported and therefore undetected an untold number of potentially high-risk, pre-cancerous growths."
However Dan Johnson, MD, of the Mayo Clinic (Scottsdale Arizona) and principal investigator in the trial, told Diagnostics & Imaging Week that polyps smaller than 5 mm in diameter are likely to have "only a 1% chance" of becoming cancerous and thus it is not worth looking at what he called "all the bumps and lumps" in the colon and to follow-up with unnecessary biopsy procedures.
"That's not just our opinion," Johnson said, but that the polyp target for the study was determined based on the use of national guidelines.
Further responding to the National CT Colonography Trial, the ACG's statement outlined several other caveats about ACRIN's conclusions.
• that there is great value in a standard colonoscopy combined with a procedure to remove a precancerous polyp, in a single intervention, thus offering a "preventive" strategy;
• that CTC comes with radiation exposure, producing a long-term risk for cancer — citing the FDA as categorizing X-ray exposure as a carcinogen (the ACRIN Q&A acknowledges this risk, saying that a CTC exam is "reported" to use 50% less radiation than a standard CT scan of the abdomen or pelvis);
• that though less-invasive, CTC should not be presented to patients as being without pain or discomfort – that it requires "the same bowel preparation" as colonoscopy and that it involves the insertion of a tube and insufflation of the abdomen with gas, thus not a "painless or risk-free procedure ... ."
The ACRIN statement did not duck the need for needing "to clear and cleanse the colon" in CTC.
But Johnson said that after the initial colon preparation the procedure is "a piece of cake," allowing the patient to drive himself/herself home or to work the same day.
In the study, 99% of participants had a CTC, followed by the standard colonoscopy, the same day.
He said that the study does not seek to supplant standard colonoscopy with CTC, but should actually increase the number of standard procedures by finding more early cancers.
The broad hope by advocates of virtual colonoscopy – emphasized to D&IW by Johnson — is that because CTC is less anxiety-provoking less uncomfortable for patients, it will result in more scanning for the disease and thus earlier treatment and reduced mortality.
Colorectal cancer is the third most frequently diagnosed cancer and second leading cause of cancer death in men and women in the U.S.
Recommendations encourage adults over the age of 50 to receive a colonoscopy every 10 years, or more frequently. But while the benefits of colorectal screening are well publicized, the majority of those seen as benefitting from the procedure do not get this screening.
Importantly, ACRIN does not downplay the value of colonoscopy or say that CTC would supplant the standard procedure.
Paul Limburg, MD, study author and gastroenterologist at the Mayo Clinic (Rochester, Minnesota), said, "There are clearly clinical settings in which CT colonography, colonoscopy, or both tests in combination offer distinct advantages. The most important advice we can give to patients is to get screened. How they get screened should be an individual decision based upon discussions between patients and their providers."
Shawn Farley, spokesperson for ACRIN, told D&IW that estimates he has seen indicate that CTC costs are about half that of standard colonoscopy, with private reimbursement for CTC about $1,000, and costs for standard colonoscopy as much as $3,000.