Why is sDNA now recommended, and what are its strengths and limitations?

sDNA testing is a relatively new method of colorectal cancer screening. Cancer cells that contain altered DNA are continuously shed into the large bowel and passed in the feces, and this altered DNA can be isolated and identified through this screening test. In previous assessments, both the American Cancer Society and the U.S. Multi-Society Task Force concluded that data were insufficient to recommend screening with sDNA for average risk individuals. Based on the accumulation of evidence since the last update of these guidelines in 2003, there is sufficient data to conclude that sDNA testing meets the threshold criterion of detecting the majority of prevalent and incident cancers at the time of testing.

Advantages of this method are that sDNA testing has acceptable sensitivity for colorectal cancer, is not dependent on the detection of occult blood, which is intermittent, and requires only a single episode of stool collection. sDNA also is noninvasive, and lacks physical harm. Patient and provider acceptance of this technique appears to be high.

A clear limitation of sDNA testing is that test sensitivity is based on a panel of markers that appears to identify most, but not all, colorectal cancers. Further, it is not known what proportion of advanced adenomas is identified with the current commercially available version of the stool DNA test. Patients therefore need to be informed that the current test will detect some but not all cancers and some polyps. Also, there is uncertainty about how positive results without evidence of advanced lesions or cancer on follow-up colonoscopy should be interpreted by patients, and whether or not these patients require a different plan for on-going surveillance. Other potential limitations that have considerable implications for cost-effectiveness are the unit cost of the test, which is considerably higher than the other stool tests, and the frequency with which the test should be performed, which is uncertain.