Circulating Methylated SEPT9 DNA in Plasma Is a Biomarker for Colorectal Cancer

Background: The presence of aberrantly methylated SEPT9 DNA in plasma is highly correlated with the occurrence of colorectal cancer. We report the development of a new SEPT9 biomarker assay and its validation in case–control studies. The development of such a minimally invasive blood-based test may help to reduce the current gap in screening coverage. Methods: A new SEPT9 DNA methylation assay was developed for plasma. The assay comprised plasma DNA extraction, bisulfite conversion of DNA, purification of bisulfite-converted DNA, quantification of converted DNA by real-time PCR, and measurement of SEPT9 methylation by real-time PCR. Performance of the SEPT9 assay was established in a study of 97 cases with verified colorectal cancer and 172 healthy controls as verified by colonoscopy. Performance based on predetermined algorithms was validated in an independent blinded study with 90 cases and 155 controls. Results: The SEPT9 assay workflow yielded 1.9 μg/L (CI 1.3–3.0) circulating plasma DNA following bisulfite conversion, a recovery of 45%–50% of genomic DNA, similar to yields in previous studies. The SEPT9 assay successfully identified 72% of cancers at a specificity of 93% in the training study and 68% of cancers at a specificity of 89% in the testing study. Conclusions: Circulating methylated SEPT9 DNA, as measured in the new mSEPT9 assay, is a valuable biomarker for minimally invasive detection of colorectal cancer. The new assay is amenable to automation and standardized use in the clinical laboratory.