Methylated biomarkers for breast cancer identified through public database analysis and plasma target capture sequencing.

BACKGROUND: Aberrant methylation is common during the early stage of cancer development. This study was designed to investigate DNA methylation as biomarker for breast cancer. METHODS: Public database analysis and methylation-specific whole-gene sequencing were conducted to identify methylated biomarkers that would enable early non-invasive diagnosis of breast cancer. Firstly, the data was obtained from the TCGA Database and the Blueprint Epigenome Database. Secondly, methylation-specific whole-gene sequencing was conducted in 10 female patients with early-stage breast cancer and 10 healthy female volunteers from Nanfang Hospital of Southern Medical University between March 2018 and July 2018. Thirdly, the R language was used for data analysis, and KEGG and DAVID online tool was used for annotations. RESULTS: We found that methylation levels at 13 cytosine-phosphate-guanine (CpG) sites (cg04066177, cg04281344, cg05995576, cg06221609, cg08642731, cg11388802, cg12665414, cg14557216, cg19404723, cg19457909, cg24570211, cg25818763, and cg26215982) in the malignant tissue DNA were highly comparable to those of circulating cell-free DNA (cfDNA) of breast cancer patients, but were significantly different from those of normal tissue DNA, cfDNA of healthy women, and leukocyte DNA. In addition, three CpG sites (cg04281344, cg24570211, and cg26215982) were confirmed in clinical research, which showed that the sensitivity and specificity of these CpGs as biomarkers for breast cancer were 69.4-83.7% and 85.7-88.6%, respectively. CONCLUSIONS: New biomarkers were identified and confirmed for breast cancer by comparing the methylation of tumour tissues, leukocytes, and non-plasma DNA.