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Stool DNA Testing to Detect Colorectal Neoplasia

An emerging technique for colorectal cancer screening is the detection of altered DNA in exfoliated cells in the stool. Mayo Clinic researchers examined the accuracy of a panel of stool assays that targeted DNA abnormalities associated with colorectal neoplasia: point mutations in the K-ras, p53, and APC genes; the Bat-26 marker of microsatellite instability; and "long" DNA.

The stool tests were performed on 22 patients with known colorectal cancer (13 of the cancers were Dukes' A or B), 11 patients with known adenomas at least 1 cm in size, and 28 controls with normal colonoscopy results. One or more of the fecal DNA assays was positive in 20 of the 22 cancer patients (sensitivity, 91 percent) and in 9 of 11 adenoma patients (sensitivity, 82 percent). Among the 28 normal controls, there were only 2 false-positive results (specificity, 93 percent). The K-ras marker was responsible for both false positives; removing it from the panel would have boosted specificity to 100 percent while preserving a 91 percent sensitivity for cancer and a 73 percent sensitivity for adenoma. Notably, a standard occult blood test was negative in all patients with adenomas.

Comment: Stool testing for altered DNA is a promising alternative to current methods of colorectal cancer screening, particularly if these sensitivities and specificities can be duplicated in other populations and if improved clinical outcomes can be demonstrated. Because of the numerous DNA abnormalities associated with neoplasia, inexpensive multitarget assays are needed for optimal screening.

— AS Brett

Published in Journal Watch General Medicine November 21, 2000

Citation(s):

Ahlquist DA et al. Colorectal cancer screening by detection of altered human DNA in stool: Feasibility of a multitarget assay panel. Gastroenterology 2000 Nov 119 1219 -1227.

• Medline abstract (Free)