Methylome Analyses Implicate Fallopian TubeEpithelia as theOrigin forHigh-GradeSerous Ovarian Cancer

High-grade serous ovarian cancer (HGSC) is themost common and lethal form of epithelial ovarian cancer (EOC). Two distinct tissues have been suggested as the tissue of origin: ovarian surface epithelia (OSE) and fallopian tube epithelia (FTE). We hypothesized that the DNA methylome of HGSC should more closely resemble the methylome of its tissue of origin. To this end, we profiled HGSC (n1⁄4 10), and patient-matched OSE and FTE (n1⁄4 5) primary fresh-frozen tissues, and analyzed the DNA methylome using Illumina 450K arrays (n1⁄4 20) and Agilent Sure Select methyl-seq (n 1⁄4 7). Methylomes were compared using statistical analyses of differentially methylated CpG sites (DMC) and differentially methylated regions (DMR). In addition, methylation was evaluated within a variety of different genomic contexts, including CpG island shores and Homeobox (HOX) genes, due to their roles in tissue specification. Publicly available HGSC methylome data (n 1⁄4 628) were interrogated to provide additional comparisons with FTE and OSE for validation. These analyses revealed that HGSC and FTE methylomes are significantly and consistentlymore highly conserved than areHGSCand OSE. Pearson correlations and hierarchal clustering of genes, promoters, CpG islands, CpG island shores, and HOX genes all revealed increased relatedness of HGSC and FTE methylomes. Thus, these findings reveal that the landscape of FTEmore closely resembles HGSC, the most common and deadly EOC subtype. Implications: DNA methylome analyses support the hypothesis that HGSC arise from the fallopian tube and that due to its tissuespecificity and biochemical stability, interrogation of the methylomemaybe a valuable approach to examine cell/tissue lineage in cancer. Mol Cancer Res; 14(9); 1–8. 2016 AACR.