Looking at more than 10,000 screening CT colonography or virtual colonoscopy exams, doctors found cancers in 1 in every 200 patients, but more often those cancers were not colorectal cancer, but unsuspected cancer found outside the colon.
The tests found 22 colorectal cancers (1 in every 500 patients examined) and 36 other cancers (1 in every 300 patients.) More than half were found at an early stage I. After an average follow-up time of 30 months, only 3 patients had died of cancer.
Renal cell cancer was the most frequent extracolonic cancer, discovered in 11 patients who didn’t have symptoms. Eight lung cancers were also found along with six cases of non-Hodgkins lymphoma and eleven cancers in other sites. More specific information about patients, their cancers, and their survival is part of the report in Radiology.
CT colonography allows radiologists limited views of the body outside of the colon, particularly in the pelvis, abdomen, and part of the lungs. About 6 percent of the time, the exam leads to additional testing for other diseases, although more than half of that testing will eventually prove benign.
If polyps or suspected colorectal cancer is found during CTC screening, referrals are necessary for a traditional optical colonoscopy where polyps can be removed and biopsied.
During an exam patients are exposed to about 10 millisieverts (mSv) of radiation, about the same amount they receive from normal background radiation in three years.
In a news release from the Radiological Society of North America (RSNA), lead author Perry J. Pickhardt, M.D., professor of radiology and chief of GI Imaging, at the University of Wisconsin School of Medicine & Public Health, noted,
We are finding that virtual colonoscopy screening actually identifies more unsuspected cancers outside of the colon than within it. As with asymptomatic colorectal cancers identified by virtual colonoscopy screening, these cancers are often detected at an early, curable stage.
However, he points out that CT colonography does find benign conditions that nevertheless need follow-up.
Although extracolonic evaluation at screening CT colonography does carry some disadvantages, such as patient anxiety, inconvenience, or the potential for benign biopsy, our results suggest that early detection of asymptomatic extracolonic cancer represents an additional benefit of screening CT colonography that is not available with optical colonoscopy
Reporting their results in the April issue of Radiology, Pickhardt and his colleagues concluded,
The overall detection rate of unsuspected cancer is approximately one per 200 asymptomatic adults undergoing routine screening CT colonography, including about one invasive CRC per 500 cases and one extracolonic cancer per 300 cases. Detection and treatment at an early presymptomatic stage may have contributed to the favorable outcome.
RSNA News Release: Virtual Colonoscopy Allows Detection of Unsuspected Cancers Beyond Colon, March 23, 2010.