Abstract 4922: Chronic diseases and age >65 years may cause false positive results in colorectal cancer screening with the blood-based Sept9 methylation assay

Abstract

Abstract The aim of this study was to investigate whether the performance of the colorectal cancer (CRC) screening marker Sept9 was influenced by comorbidities and/or demographic characteristics. Annually, CRC is diagnosed in >1.4 million subjects worldwide and incidence is increasing. Much research is therefore directed at CRC screening, which has proven to reduce cancer-related mortality. The Sept9 DNA-methylation assay is among the most well studied blood-based epigentic screening markers. However, currently we have only limited knowledge of how comorbidities and/or demographic characteristics influence assay performance, as this has not been part of earlier study objectives. Using a retrospective nested case-control study design fulfilling the REMARK criteria, we studied plasma from 149 cancers and 150 controls selected from a well-characterized cohort of 4698 subjects referred for diagnostic colonoscopy due to CRC-related symptoms. The cohort had a wide variety of comorbidities. Cases and controls were matched on age and gender, and cases were further stratified by tumor-site and tumor-stage. Plasma Sept9 levels were assessed using a commercially available qMSP based assay in the most specific setting; the cut-off value was set at 2 positive out of 3 replicates (2/3 algorithm). STATA V.12.1 was used for statistical analysis. Fishers exact test and logistic regression were used to estimate the association between Sept9 results and CRC. With the specific 2/3 test algorithm, clinical sensitivity for CRC stages I-IV was 17%, 74%, 63%, and 86%, and the overall sensitivity 59% (95% CI, 64-80%) and specificity 95% (95% CI, 91-98%), respectively. Sensitivity for adenomas was 0% (95% CI, 0-16%). Age >65 was significantly associated with both increased false positive ((p<0.05) and false negative results (p = 0.007). Arthritis was associated with a higher false negative rate (p = 0.07) and arteriosclerosis was significantly associated with a higher false positive rate (p = 0.007). Diabetes was associated with Sept9 positivity with an OR of 4.7 (95% CI 1.5-14.5). In a multivariate logistic regression, adjusting for the associated comorbidities and age >65, the OR for a positive Sept9 test to be associated with CRC increased from 21 (95% CI 9-47) to 117 (95% CI 26-528). The results indicate that the Sept9 assay is not only affected by CRC stage, but by several comorbidities and age >65 as well; these are factors commonly associated with CRC screening populations. The findings are of importance not only if the Sept9 assay is used as a single marker for CRC screening: it may also have a wider impact, as it is likely that such factors may affect other blood-based methylation markers as well. We hypothesize that an increased plasma input might increase assay sensitivity and that multiplexing of several biomarkers may diminish false positive results in blood-based screening with methylation specific markers. Citation Format: Mai-Britt W. Ørntoft, Hans Jørgen Nielsen, Torben Falck Ørntoft, Claus Lindbjerg. Chronic diseases and age >65 years may cause false positive results in colorectal cancer screening with the blood-based Sept9 methylation assay. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4922.