Specificity of methylated BCAT1 and IKZF1 for colorectal cancer.

Abstract

580 Background: 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 positivity rates were significantly higher in CRC (126/212, 59.4%, 95% CI: 52.5 - 66.1) and oesophageal cancer (6/16, 33.3%, 11.0 - 58.7) cases only compared to controls (16/245, 6.5%, 3.8 - 10.4; p < 0.01). ctDNA was more likely to be positive in late stage cancers, although only significant for CRC, Table. Cancer tissue positivity rates were: CRC, 15/15, 100% (96.4 - 100); oesophageal, 5/6, 83.3% (35.9 - 99.6); prostate, 4/9, 44.4% (13.7 - 78.8); breast, 5/26, 19.2% (6.6 - 39.4). All cancer tissues had significantly higher methylation levels than the adjacent tissue (Chi2 test, p >0.05). Conclusions: Only colorectal and oesophageal cancer patients had significantly higher ctDNA positivity rates (using methylated BCAT1/IKZF1) compared to controls. This was also reflected in a higher proportion of cases showing methylation in the cancer tissue. The methylated BCAT1/IKZF1 blood test should be investigated further as a screening and surveillance tool for oesophageal cancer. [Table: see text]