Genome-wide DNA methylation profiles of endometrioid endometrial cancer tissue

Genome-wide DNA methylation screening was performed using the Infinium MethylationEPIC BeadChip in 49 fresh-frozen tissue samples and 31 formalin-fixed paraffin-embedded tissue samples obtained from surgically resected materials of patients with endometrioid endometrial cancer. Five-hundred-nanogram aliquots of DNA extracted from fresh frozen tissue samples were subjected to bisulfite conversion using an EZ DNA Methylation-Gold Kit (Zymo Research, Irvine, CA). For FFPE tissue samples, 50 to 300-nanogram aliquots of DNA were used and DNA restoration was performed using an Illumina HD FFPE Restoration Kit (Illumina). DNA methylation status at 866,895 CpG loci was examined at single-CpG resolution using the Infinium MethylationEPIC BeadChip (Illumina). After hybridization, the specifically hybridized DNA was fluorescence-labeled by a single-base extension reaction and detected using an iScan reader (Illumina) in accordance with the manufacturer’s protocol. The data were then assembled using GenomeStudio methylation software (Illumina).