A recent article in the British journal, The Lancet reported on a study by the UK Special Interest Group in Gastroenterology and Abdominal Radiology (SIGGAR….thank goodness another acronym) comparing virtual colonoscopy, also called computerized tomographic colonography (CTC) and colonoscopy. The study included 1580 patients considered high risk for colon cancer because of bleeding, pain or change in stool habits. (Although please remember that above the age of 50 we are all at risk… colon cancer is the third most prevalent cause of cancer deaths in women, after lung cancer and breast cancer.) Half of the patients were assigned to CTC and the other half to colonoscopy. The “yield” i.e., the finding of colon cancer or large polyps that are often precursors to colon cancer was nearly identical in the two groups (10.7% with CTC vs. 11.4 % with colonoscopy). The number of patients with pre-malignancies and malignancies seems high, but the individuals in the study had significant symptoms and were not simply being screened. The take home message (well perhaps polyps are not what we want to take home…) that was deemed important was the fact that both tests were comparable when it came to finding pathology. But before the Lancet commentators felt that all is well in the virtual realm of diagnosis they pointed out that 30 % of patients who underwent CTC were subsequently referred for colonoscopy and biopsy whereas “only” 8.2 % of patients in the colonoscopy group needed further investigation, mainly due to incomplete colonoscopies. Furthermore in the trial 7-10% of patients who had CTC had findings that were outside of the colon and these resulted in the need for additional testing. (CT scan surveys of large areas of the body often detail findings that may have no impact on a patient’s health. Once out there, the report mandates further work up. On the overall public health scale. this is not considered cost- effective. Aside from cost, many of these patients who now have incidental or accidental findings will undergo unnecessary, stressful and perhaps invasive testing. A few will benefit with early diagnosis and treatment of a disorder that they and their physicians did not know they had. For those few, further testing was “worth it”. But insurance companies and health care organizations don’t think that a full body scan to search for an unknown and non symptomatic “something” is an appropriate use of health resources.)
Back to recommendations…CTC does not require anesthesia. It is less invasive than colonoscopy and will not cause complications such as perforation and bleeding. And, it is less expensive. The Lancet and other studies have shown that the “miss rates” with CTC for large polyps and cancer are low. CTC may, however, miss very small polyps. When considering the pros and cons of virtual vs. “in there” colonoscopy remember that if a polyp is found on CTC it mandates a referral (and another prep) for the full colonoscopy, so that a biopsy can be done. The current estimate is that during low risk screening, this will occur in 5 % of patients. Finally, CTC is currently not covered by insurance.
My preference for most of my patients is that their first screening procedure for colorectal cancer be done via actual colonoscopy at age 50 (earlier if there is a family history of early onset colon cancer, a history of inflammatory bowel disease or other factors that increase risk.) Once the absence of polyps is confirmed and there is no family history of colon cancer, repeat screening 10 years later with CTC is a reasonable option. And who knows, by then there may be even simpler, non prep requiring tests such as DNA screening of stool for precancerous or cancer mutations.