Methylated BCAT1 and IKZF1 DNA in tissue and plasma from colorectal cancer cases.

Abstract

543 Background: We have previously described a 2-gene blood test based on the detection of methylated BCAT1 and IKZF1 for colorectal cancer (CRC). This study explored the relationship between the presence of these methylated DNA biomarkers in plasma and tissue from CRC patients. Methods: Blood (pre-resection) and samples of tumor and adjacent non-cancer tissue (NCT) were collected from 75 patients diagnosed with CRC. Extracted DNA was assessed for presence of methylated BCAT1 and IKZF1. Results: Methylated BCAT1 and IKZF1 were detected in 68 (91%) and 69 (92%) tumor tissues, respectively, with one or both methylation biomarkers being present in 74 (99%) of the 75 tumor tissues. Combined methylation levels (mean %methylated DNA per 5ng total DNA) were significantly higher in tumor than NCT: 56% methylated DNA (95%CI: 47-67) versus 3% (2.7-4) (t-test, p < 0.001). In the matching plasma samples, methylated BCAT1 and IKZF1 were detected in 35/75 and 36/75, respectively, with a combined presence of 48/75 (64%; 95%CI: 52-75). Appearance of methylated BCAT1/IKZF1 DNA in plasma and tissue was not significantly correlated (p > 0.05). Tissue methylation levels were independent of morphology, whereas the presence of biomarkers in plasma was associated with tumor size (Chi2 p = 0.02) and depth of invasion (Chi2 p = 0.003). There was no association with tumor differentiation, lymphovascularity or lymph node invasion. The one tumor tissue sample negative for BCAT1/IKZF1 methylation was also negative in plasma. For one metastatic case, primary tumor, plasma and liver samples were available and analysed, which confirmed methylated BCAT1/IKZF1 in all samples. It is worth noting that no methylation was detected in adjacent non-cancer liver tissue. Conclusions: BCAT1 and IKZF1 are highly methylated in tumor tissues, regardless of morphology. The low methylation levels in the surrounding NCT suggest that these changes are tumor specific with no obvious field effect. Appearance of the methylated biomarkers in blood depends on the primary tumor displaying invasive morphological features indicative of the tumor having access to shedding into the blood stream.