Noninvasive Stool Test Biased by Patient's Age

A DNA methylation test for colorectal cancer (CRC) is influenced by the clinical variable age and not by drug choice or other variables.

Stool assays of carefully selected methylated gene-marker candidates yield high detection rates of both CRC and large adenomas as aberrantly methylated genes represent attractive and broadly informative markers for these forms of malignancy.

Scientists at the Mayo Clinic (Rochester, MN, USA) collected buffered stools within three years of a normal colonoscopy from 500 patients undergoing average-risk screening or polyp surveillance. The median age was 64 years old, with a range of 44-85 and 53% were women. The stool samples were promptly homogenized, aliquoted, and frozen at -80 °C.

Target genes were purified by hybrid capture from thawed and centrifuged aliquot supernatants, bisulfite treated, and assayed using the quantitative allele-specific real-time target and signal amplification the analytically-sensitive (QuARTS) method. The reference gene β-actin was assayed along with methylation of the N-Myc Downstream-Regulated gene 4 (NDRG4), Bone Morphogenetic Protein 3 gene (BMP3), the Vimentin gene, and the Tissue Factor Pathway Inhibitor 2 gene (TFPI2).

The only patient characteristic that significantly influenced all methylated marker levels in stool was age. Standardized relative change was greatest with TFPI2 at +91.3, least with BMP3 at +29.7, and intermediate with vimentin at +46.0 and NDRG4 at +45.1. David Ahlquist, MD, professor of medicine at the Mayo Clinic, said, "There was a progressive increase in background methylation levels that varied widely between methylation markers tested as a patient aged. For example, median background methylation levels of the TFPI2 gene increased 49% in patients from age 50 to age 80, whereas levels for the BMP3 gene increased by only 0.2% across this age range." The study was presented at the American Association for Cancer Research Annual Meeting, held March 31 - April 4, 2012, in Chicago (IL, USA).

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