An FDA panel yesterday agreed that computed tomography colonography should be a screening option offered to asymptomatic colorectal cancer patients over age 50.
The Gastroenterology-Urology Devices Panel and the Radiological Devices Panel said there is a benefit to CTC screening for asymptomatic patients, but voiced concerns over giving patients with negative screens a false sense of security due to insufficient biological data on lesions between 6mm and 9mm, which CTC does not detect as effectively.
For one, CTC is less invasive than colonoscopy, which is likely to encourage patients to get screened. And patients do not have to miss as much work time, nor ask someone else to miss work due to the sedation or anesthesia that accompanies colonoscopy, panelists said.
"From what I’ve seen today there is increased patient acceptance," said Dr. Edward Dauer of Florida Medical Services in Ft. Lauderdale. "Patients are more likely to undergo screening with a CTC, although the problem is the smaller lesions 6mm-9mm and under 6mm are not as readily detectable. Those also have more time to be detected the next time.
"In the [American College of Radiology Imaging Network trial] series we saw that there was a 90% sensitivity for lesions 1 cm and above, which is our important finding, and the perforation rate and complications were very low," Dauer said. "So all in all, there seems to be increased patient acceptance, very good sensitivity and selectivity."
Colorectal cancer risks, current recommendations
Colorectal cancer is the 4th-most common cancer and the second leading cause of cancer death in the U.S., according to the federal watchdog agency. This year, nearly 143,000 people will likely be diagnosed with colon cancer and nearly 51,000 will die from the disease.
The "vast majority" of colon cancers develop from colonic polyps, meaning timely removal of the pre-cancerous lesions can prevent colorectal cancer from developing, the FDA said.
And the survival rate for patients in whom colorectal cancer is detected early is significantly higher, with a 5-year survival rate of 90.3% for localized colorectal cancer compared with 12.5% in cases where the cancer has metastasized elsewhere in the body.
The U.S. Preventive Services Task Force recommends universal screening for colorectal cancer starting at age 50 for persons without colorectal cancer risk factors and has listed annual fecal occult blood testing, optical colonoscopy every 10 years, and sigmoidoscopy every 5 years combined with FOBT every 3 years as equally effective screening regimens for the disease, the FDA noted.
Other screening tests for colorectal cancer include CTC, immunochemical FOBT, double-contrast barium enema and DNA stool assays.
But compliance with colorectal cancer screening is low, despite the task force’s recommendation, with only 58.6% of eligible adults following screening recommendations, according to the Centers for Disease Control & Prevention.
Panel: Extracolonic findings a plus
CTC, unlike the other screening methods, can detect incidental findings in other organs, including the kidneys, parts of the lungs, the abdominal aorta and other intra-abdominal organs, according to the FDA. Although these "extracolonic" findings can detect serious illnesses beside colon cancer, they also carry the risk of false positives requiring further testing.
"The extracolonic findings are the cherry on the top of the sundae for CT colonoscopy," Dr. Leonard Glassman of Washington Radiology Assoc. in Washington said. "They’re the lifesavers that we didn’t expect to get. They’re the small renal tumors, they’re the abdominal aortic aneurisms, they’re the person who goes to the emergency room knowing they have a left renal stone, or even better a right renal stone, rather than acute colycystitis because they were told from this test. Those are pluses, not minuses."
The rest of the panel generally agreed that the benefits of extracolonic findings from CTC far outweigh any risk of unnecessary testing or procedures from false positives, saying the risks can be mitigated with proper training on the technology. And the radiation risk for patients undergoing CTC every 5 years is "very low."
Concerns about CTC
Dr. Aline Charabaty of Georgetown University said she was concerned about how CTC would be applied in the community, because data so far has come from expert radiologists who ship patients with positive screens out for endoscopy the same day.
In a real-world setting, a patient would likely need to come back another day and undergo the probe again to get a polyp removed and may fail to do so, she pointed out.
Another question mark about CTC is the issue of polyps between 6mm and 9mm "where we feel they’re not important at that time," Dr. Charabaty added. "My concern is this going to give a false sense of security to patients that, ‘My CTC was fine.’ We all have patients that have polyps and we tell them come back in 5 years and they show up 10 years later, even for those patients that know they had a polyp and an adenoma that was removed."
Data are scarce on whether colonoscopy’s effect on bursting polyps smaller than 1 cm in size actually reduces colon cancer, the panel noted, and they asked that more information on these smaller lesions be gathered to provide greater insight into their biology and improve overall screening practices.
The panel recommended that CTC screening be offered as an option for asymptomatic patients, on par with the other task force-recommended colon cancer screening methods, but emphasized that quality control measures are key, including accreditation of the reader and standardization of the procedure.
The panel’s recommendation opposes a May 2009 Medicare decision not to extend coverage to CT colonography, also known as virtual colonoscopy, for colorectal cancer screening.