Abstract 3572: Methylated gene marker levels in stool: effects of demographic, drug, and body mass and other patient characteristics

Abstract

Abstract Aberrantly methylated genes represent attractive and broadly informative markers for colorectal cancer (CRC). As demographics, numerous ingestants, environmental exposures, and obesity variably influence both gene methylation rates and CRC incidence, it is important to understand the effects of such covariates on the clinical performance of CRC screening tests that incorporate assay of methylated gene markers. Based on a recent multicenter study (Ahlquist et al. Gastroenterology 2012 (in press)), stool assay of carefully selected methylated gene marker candidates (NDRG4, BMP3, vimentin, TFPI2), alone or in combination, yield high detection rates of both CRC and large adenomas. Aim: To assess the impact of demographic, exposure, body mass, and other patient variables on stool levels of the above 4 methylated gene markers. Methods: We studied buffered stools collected within 3 years of a normal colonoscopy from 500 patients undergoing average-risk screening or polyp surveillance (median age 64 (range 44-85); 53% women). Upon receipt, stools were promptly homogenized, aliquoted, and frozen at –80°C. On supernatants from thawed/spun aliquots, target genes were purified by hybrid capture, bisulfite treated, and assayed using the analytically-sensitive QuARTS method (quantitative allele-specific real-time target and signal amplification), as described (above citation). The reference gene β-actin was assayed along with methylation of NDRG4, BMP3, vimentin, TFPI2. Log-converted data were normalized to allow comparison of effects between markers, and effect size was expressed as % change relative to standard deviation for each marker (standardized relative change (SRβ)). Results: The only patient characteristic that significantly influenced all methylated marker levels in stool was age (p<0.0001 for each marker); SRΔ was greatest with TFPI2 at +91.3 (p<0.001 vs other markers), least with BMP3 at +29.7 (p<0.001 vs others), and intermediate with vimentin at +46.0 and NDRG4 at +45.1. In contrast to methylation markers, levels of β-actin did not change across age. The other demographic variables of sex, race, and geographic residence had no effect on methylation markers. Marker levels were also not affected by exposure variables (smoking, alcohol consumption, or analgesic use), by family history of CRC or polyps, or by personal history of polyps. Finally, neither overweight status (n=176) nor obesity (n=148) had an effect on marker levels. Conclusions: Age significantly affects stool levels of tumor-associated methylated gene markers in colonoscopy-normal patients, and the degree of this age effect differs across markers. In contrast, other key patient variables had no effect on stool marker levels. Comment: Optimal use of these methylation markers for stool screening of CRC may require age-adjustment of normal cutoff levels to maximize test specificity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3572. doi:1538-7445.AM2012-3572