Use of DNA methylation to distinguish gallbladder carcinoma.

Abstract

e15605 Background: Gallbladder cancer (GBC), an uncommon malignancy with a high mortality rate, is often diagnosed late due to lack of early symptoms and the relative hidden nature of the gallbladder. Despite the advancements in imaging technologies, there is no reliable screening test for GBC. The role of aberrant DNA methylation in the process of tumorigenesis both at individual genes and a genome-wide scale has been well elucidated. It occurs very early in cancer development, thus capable of serving as a screening marker. Methods: Panel Design: Methylation data of tumor samples (12 types, n = 4,772), adjacent normal (8 types, n = 411), and normal white blood cells (n = 656) from TCGA and GSE were compared. Differentially methylated sites were derived using a Bayesian hierarchical model-DSS with an adjusted p-value < 0.05. Our panel covers 80,672 CpG sites, spanning 1.05Mb of human genome. This panel contains 12,196 GBC relevant CpG sites. We performed targeted bisulfite sequencing on 23 GBC patients (6 stage II-III, 17 stage IV) and 13 patients with non-malignant gallbladder diseases (cholecystitis and gallstones). Of the 23 GBC patients, we obtained adjacent normal tissue from 7 of them. Basic clinical features such as age, gender, of patients with GBC and patients with non-malignant gallbladder diseases were comparable. Results: Among the 12,196 GBC relevant CpG sites, 10,216 sites were statistically significantly hypermethylated and 275 sites were statistically significantly hypomethylated comparing to patients with non-malignant gallbladder disease as well as adjacent normal gallbladder tissues. Subsequently, we used the derived differentially methylated CpG sites to construct a linear regression model, achieving an area under curve of 99%. Collectively, the methylation levels were comparable between tissues with non-malignant disease and adjacent normal. Interestingly, when considering the 275 hypomethylated markers alone, we observed that the methylation level of adjacent normal tissues is significantly higher than tissues with non-malignant disease. Conclusions: Collectively, our panel can effectively distinguish GBC samples from non-cancerous samples, demonstrating the potential of DNA methylation in GBC screening. Furthermore, hypomethylation markers can be used to distinguish non-malignant disease from the healthy.