LAUSR

580Background: Methylated BCAT1 and IKZF1 are useful circulating tumor DNA (ctDNA) biomarkers for detection and following the course of colorectal cancer (CRC). This study aimed to determine the specificity of methylated BCAT1/IKZF1 for CRC detection by assaying specimens from patients with other adenocarcinomas. Methods: Blood was collected from patients with invasive adenocarcinoma of the prostate (n = 32), breast (16), oesophagus (15) or colon/rectum (212), prior to any treatment or resection, and from 245 clinically assessed controls with no known prior or current adenocarcinoma. Biopsies were collected from cancer tissue and adjacent non-neoplastic tissue either prior to treatment or at surgery from 9 prostate, 26 breast, 6 oesophagus, 15 CRC cases. All specimens were assayed for methylated BCAT1 and IKZF1 DNA. Calculation of positivity rates: tissue, the proportion of tissue cases with ≥ 5% methylation; blood, the proportion of cases with any detectable signal of either marker. Results: ctDNA positi...