Correlation of LINE-1 hypomethylation with size and dysplasia in colorectal tubular adenomas, and risk for synchronous and metachronous CRC.

Abstract

e16083 Background: Conventional adenomas (tubular or tubulovillous adenoma; TA) are frequently detected in patients undergoing average risk screening colonoscopy. Risk stratification of adenomas is currently limited to histologic features and size. Molecular features of TA could help further determine risk for development of CRC. Here, we report whether size of TA, high grade dysplasia, and synchronous or metachronous CRC associate with LINE-1 methylation. Methods: LINE-1 methylation was assessed by pyrosequencing of bisulfite-converted DNA. We compared LINE-1 methylation in TA among varying sizes, in the presence of high or low grade dysplasia, and between patients with synchronous and metachronous colorectal cancer. Results: LINE-1 methlyation was found to progressively decrease in TA of increasing size and with high grade dysplasia. TA < 5mm in size (n = 45) had higher LINE-1 methylation levels compared to TA 5-9mm in size (n = 42), and > = 10mm (n = 32) (72.31 ± 6.11 vs 67.50 ± 7.00 vs 66.75 ± 11.89, p = 0.013). TA with high grade dysplasia (n = 26) had lower LINE-1 methylation levels compared to low grade dysplasia (n = 135) (59.86±7.93 vs 67.16±9.20, p < 0.001). Tumor tissue (n = 36) had the lowest levels of LINE-1 methylation at 50.36±8.40. There were lower levels of LINE-1 methylation in TA of patients with synchronous CRC compared to those without (53.07+4.5 vs 59.95+5.4 vs, p < 0.001). LINE-1 methylation was lower in normal tissue from cancer patients compared to that from patients without any neoplasia (50.36 ± 8.40 vs 71.50 ±6.47, p < 0.001). LINE-1 methylation levels were higher in patients with initial low risk TA who developed metachronous high risk TA (n = 31) compared to those who did not (n = 35) (75.78±2.45 vs 64.84±4.58, p = 0.001). LINE-1 methylation levels were not different in patients with initial TA who developed metachronous CRC (n = 2) compared to those who did not (n = 89) (70.00±5.65 vs 66.85±8.20, p = 0.69). Conclusions: High-grade dysplasia and increasing size of conventional TA were associated with greater LINE-1 hypomethylation. This is supportive of a hypothesis that greater LINE-1 hypomethylation of tubular adenomas indicates advancement along the CRC tumorigenesis pathway. Greater LINE-1 hypomethylation in TA was also seen in patients with synchronous CRC compared to those without, though no difference was found in those who developed metachronous CRC. Higher LINE-1 methylation was seen in patients with initial low risk TA, who developed metachronous high risk TA compared to those who did not.