Septin 9 methylated DNA is a sensitive and specific blood test for colorectal cancer

Abstract

Background: About half of Americans 50 to 75 years old do not follow recommended colorectal cancer (CRC) screening guidelines, leaving 40 million individuals unscreened. A simple blood test would increase screening compliance, promoting early detection and better patient outcomes. The objective of this study is to demonstrate the performance of an improved sensitivity blood-based Septin 9 (SEPT9) methylated DNA test for colorectal cancer. Study variables include clinical stage, tumor location and histologic grade.

Methods: Plasma samples were collected from 50 untreated CRC patients at 3 institutions; 94 control samples were collected at 4 US institutions; samples were collected from 300 colonoscopy patients at 1 US clinic prior to endoscopy. SEPT9 methylated DNA concentration was tested in analytical specimens, plasma of known CRC cases, healthy control subjects, and plasma collected from colonoscopy patients.

Results: The improved SEPT9 methylated DNA test was more sensitive than previously described methods; the test had an overall sensitivity for CRC of 90% (95% CI, 77.4% to 96.3%) and specificity of 88% (95% CI, 79.6% to 93.7%), detecting CRC in patients of all stages. For early stage cancer (I and II) the test was 87% (95% CI, 71.1% to 95.1%) sensitive. The test identified CRC from all regions, including proximal colon (for example, the cecum) and had a 12% false-positive rate. In a small prospective study, the SEPT9 test detected 12% of adenomas with a false-positive rate of 3%.

Conclusions: A sensitive blood-based CRC screening test using the SEPT9 biomarker specifically detects a majority of CRCs of all stages and colorectal locations. The test could be offered to individuals of average risk for CRC who are unwilling or unable to undergo colonscopy.

Figure 1

Comparison of the Improved SEPT9 PCR Detection Protocol with the PRESEPT Method using Analytical Specimens. Methylated SEPT9 DNA was measured in pooled normal human plasma spiked with various concentrations of wholly methylated human DNA. Multiple samples of each DNA concentration were prepared and pooled, allowing for the direct comparison of the PRESEPT and improved PCR detection methods using identical DNA substrates. PCR, polymerase chain reaction.

Figure 2

Sensitivity of the SEPT9 Blood-Based Test in Clinical Case-Control Study of 144 Subjects. Methylated SEPT9 DNA was measured in plasma specimens donated by CRC patients and colonoscopy-confirmed control subjects. The percent of specimens with detectable methylated SEPT9 DNA is illustrated by the solid bars. The test has been maximized for sensitivity by only requiring one out of three of the PCR replicates to have methylated SEPT9 DNA detected. The specificity of the assay is 88% under these parameters. CRC, colorectal cancer; PCR polymerase chain reaction.

Figure 3

Location of Tumors Detected by SEPT9 Blood-Based Test. The diagram illustrates the locations of the primary tumors that were detected using the blood-based methylated SEPT9 DNA test. Note that CRCs were identified throughout the large intestine, including proximal regions such as the cecum. Three of the fifty blood specimens did not have tumor locations recorded, therefore these specimens are not represented by this figure. CRC, colorectal cancer.