In their most recent guidance on colon cancer screening (CCS), the American Cancer Society indicated that although a diversity of testing methods are available, since numerous patients are declining to be screened, “the best screening test is the one you can get done.” This posture is an effort to reduce the number of unscreened persons, since when discovered early, most colon cancer is curable.
Stool DNA testing is not new. However, head-to-head clinical trials in the past decade have indicated that when compared to colonoscopy, sensitivity for detection of colon cancers and adenomas by older methods of stool DNA testing is lower. Stool DNA CCS is predicated on the fact that mutated and cancerous colonic epithelial cells are consistently excreted daily in the stool, even more commonly than blood is found. DNA panels for CCS, in theory, should be comparable to invasive screening methods, since abnormal DNA should be readily identifiable, and confirmatory colonoscopy and resection should follow. The tepid reception provided to CCS by the public is understandable: Many are put off by the preparation, expense, and inconvenience of colonoscopy. Additionally, in recently published clinical trials of persons undergoing screening colonoscopy, only a small percent actually harbor a cancer or advanced neoplasia (approximately 100 out of 3000 screenees), so it is easy to see why most folks will be correct when they think “it’s probably not me.”
Over the last decade, screening panels for stool DNA have been improved. Imperiale et al compared screening by fecal immunochemical testing (FIT) with stool DNA testing, based on a single stool sample for each, followed by colonoscopy in all patients, regardless of screening results.
Sensitivity for colon cancer was superior by DNA stool testing (92.3% vs 73.8%); similarly, sensitivity for high-grade dysplasia favored stool DNA testing (69.2% vs 46.2% sensitivity).
A positive FIT should lead to diagnostic colonoscopy; incorporation of stool DNA testing, when positive, might rightfully provide even further motivation.
Source: Imperiale TF, et al. Multitarget stool DNA testing for colorectal-cancer screening. N Engl J Med 2014;370:1287-1297.