Abstract
PL04-04
Colorectal cancer (CRC) is the second most frequent fatal cancer in the United States and almost all CRCs develop from benign colorectal adenomas (CRAs). Advanced CRAs, of which most are CRAs with diameter ≥10 mm, are those most likely to progress to CRC. Advanced CRAs and CRCs together comprise colorectal advanced neoplasia. Most CRAs, including most advanced CRAs, can be removed definitively by colonoscopic polypectomy, and >90% of early-stage CRCs are permanently cured by segmental bowel resection. CRAs and early-stage CRCs rarely cause symptoms and can be diagnosed only be screening, which is recommended for all subjects aged 50 years and older (those at average risk) without factors, such as a family history of CRC or long standing ulcerative colitis, that put them at excess risk for the disease. Subjects at excess risk for CRC should usually start being screened before the age of 50 years. Ten percent or fewer of screened average-risk individuals have advanced neoplasia. Approved CRC screening methods for those at average risk include fecal occult blood testing (FOBT), sigmoidoscopy and optical colonoscopy (OC), which is the most sensitive and specific method. FOBT is the most frequently administered CRC screening test, but adherence with the test, which involves fecal sampling, is often poor, quite apart from the poor performance characteristics of this test (see below). Capacity to perform sigmoidoscopy, an office procedure, is steadily dwindling in the United States and sigmoidoscopy does not assess the entire colon. Limitations of screening OC include complications, the need for cathartic bowel preparation beforehand, intravenous sedation during the procedure, costs and lack of availability for underserved minority populations. Computed tomographic colonography (CTC) or virtual colonoscopy is a non-invasive technique in which thin-section images of the air-distended colon are reconstructed by software into high-resolution multiplanar 2-dimensional images and 3-dimensional endoluminal images. At present, cathartic bowel preparation similar to that required before OC must precede CTC but CTC is performed without sedation. Recent reports of a multi-center US study, presented at the American College of Radiology Imaging Network fall 2007 meeting, and a University of Wisconsin screening CTC study [Kim et al. N Engl J Med 357, 1403-1412 (2007)] have definitively shown that primary CTC and OC screening strategies result in similar detection rates for advanced neoplasms. In a recent meta-analysis of CTC, sensitivity and specificity, respectively, for detection of polyps with a diameter of ≥10 mm was 85% and 97%. In comparison, the sensitivities of one-time guaiac (gFOBT) and immunochemical FOBT (iFOBT), respectively, for the detection of polyps with a diameter of ≥10 mm are 13% and 20%. The sensitivities reported for the detection of CRC by one-time gFOBT, iFOBT, OC and CTC, respectively, are 26%, 66%, 98-100% and 75-94%. Although not approved yet by the United States Preventive Health Services Task Force for CRC screening, a major role in the future for CTC with computer-aided polyp detection for population-wide screening of people at average risk for CRC is beyond doubt. Spiral CT scanners suitable for CTC are often available even in medically underserved areas although the software and radiologist expertise required for CTC are not. However, scans from geographically remote sites can be transmitted electronically to centers that have radiologists with the required expertise. Thus, CTC has the potential to become more accessible to the general population than OC, which could progressively be reserved for the small minority of those found on screening CTC to have likely advanced neoplasms, as judged by the size of the lesions. CTC, where available, has already been generally accepted as an appropriate examination for patients in whom OC could not be completed and for those in whom the risks of OC exceed the potential benefits. CRC was formerly uncommon in American Indians/Alaska Natives but incidence and mortality from the disease are steadily increasing. The Indian Health Service (IHS), which provides health care for most American Indians/Alaska Natives, is mandated to provide an annual report to Congress in compliance with the Government Performance and Results Act. The IHS now asks that its patients should be screened for CRC as in the general population and includes information about CRC screening rates in the annual GPRA report: “Are adults 50 and older being checked for colorectal cancer?” The IHS has set a target of screening 50% of all AI/AN aged 50 years and older by the year 2010. Some of the obstacles to CRC screening in the general population and the drawbacks of some of the screening tests are accentuated in American Indians/Alaska Natives receiving their care at IHS facilities. Rates of adherence with FOBT are low; many American Indians/Alaska Natives live in remote areas in homes that lack modern toilet facilities and easy access to postal services for return of FOBT cards to a laboratory for development after application of fecal samples to the cards. Sigmoidoscopy is unavailable in many facilities serving AI/AN and there is sufficient colonoscopy capability for diagnostic studies (i.e., for patients with symptoms) but not CRC screening. The University of Arizona (UA) Department of Radiology at University Medical Center (UMC) in Tucson provides a Teleradiology Service whereby digital radiographs and scans are transmitted from remote sites for interpretation by radiologists in the Department in Tucson. Through the Teleradiology Service, UMC radiologists interpret over 100,000 radiographs, CT and magnetic resonance scans, ultrasound scans and mammograms per year from over 25 outlying sites. Many Indian reservations, some as large as the state of West Virginia, occupy lands in the states of Arizona, Utah, Colorado and New Mexico. AIl living on and around the Reservation obtain their healthcare at IHS facilities, which annually see several hundred thousand American Indians/Alaska Natives. Specialist medical services, such as gastroenterology and endoscopy, are at a premium in this geographically remote and economically deprived region of the United States. The UA Department of Radiology provides state-of-the-art CTC capability and its Teleradiology Service interprets radiographs and scans from throughout Arizona including many sent from facilities serving American Indians. CTC was added to the radiological studies provided by the Teleradiology Service in late 2006. By this service, CTC scans performed at remote facilities are transmitted electronically for interpretation at UMC and the report is sent back to the referring facility all on the day that the scan was performed. Various aspects of performing CTC besides its accuracy relative to OC are under investigation. These include computer aided detection and the feasibility of administering less drastic cathartic bowel preparations before CTC without compromising sensitivity and specificity. We believe that CTC performed in one location combined with expert interpretation via teleradiology at another is another aspect of CTC performance worthy of serious consideration. This combination may be particularly applicable in underserved communities and populations where subspecialty services are scarce. An experienced CT technologist can be trained to perform a CTC in an hour. A further development of this approach would be to introduce traveling CTC scanning units.
First AACR International Conference on the Science of Cancer Health Disparities-- Nov 27-30, 2007; Atlanta, GA