Dr. Ernest Hawk is the Chief of NCI's Gastrointestinal and Other Cancers Research Group.

Who should be screened for colorectal cancer and how often?
Currently, the U.S. Preventive Services Task Force recommends that Americans aged 50 years and older be screened for colorectal cancer. Those at higher risk for cancer, as evidenced by a close relative with either adenomas or cancer, are advised to start at an earlier age. Colorectal cancer is largely a preventable illness but, unfortunately, in the United States only 30 to 40 percent of people who should be screened have been.

What is virtual colonoscopy (VC)?
VC is a new technique that uses x-rays delivered through a CT scanner to take cross-sectional views of the colon through the abdomen. Those views are then reconstructed using computer software. The result is a set of images that provides radiologists trained in this technique with essentially the same sort of view of the colon that a gastroenterologist would get using optical colonoscopy (OC), which acquires images through a tube inserted into the colon. VC is relatively quick, fairly sensitive, and only minimally invasive.

What are the benefits of VC over OC?
The speed, relatively low level of invasiveness, and potential for broad availability are major advantages of VC at the moment. VC only takes on the order of a few minutes to actually do the exam, and probably 15 to 30 minutes more to read the exam.

What are the disadvantages of VC compared to OC?
The biggest drawback is that VC is not widely available and still awaits definitive testing. Another limitation of VC relates to patients still needing to go through the same bowel preparatory regime. In addition, VC requires instrumentation to put air into the colon. These are the key issues holding VC back from being widely appreciated and implemented.