Abstract 5698: Genome-wide DNA methylation profiling for differentiating synchronous endometrial and ovarian cancer

Abstract

<p>Background: Synchronous endometrial and ovarian cancer (SEOC) refers to simultaneously discovered endometrial and ovarian tumours on the same patient. SEOC may represent double primary (DP) tumours that arise independently on the two sites, or clonally related (CR) tumours that arise either on the endometrium or ovary and metastasized to the other site. Accurate differential diagnosis between these two scenarios can implicate on the treatment options and prognostication of SEOC. However, it is difficult to achieve as the histopathological features of DP and CR tumours are often ambiguous. DNA methylation landscape of SEOC may provide markers for differentiating DP and CR tumours but remain largely unexplored.</p><p>Methods: The archival tissues of six pairs of SEOC and their accompanied normal uterine tissues were retrieved. The tumours were accessed by conventional histopathological criteria and mitochondrial DNA (mtDNA) sequencing to categorize them into DP or CR. We then analyzed the methylation profiles of >850,000 CpG sites of the tumor samples using the Illumina Infinium MethylationEPIC BeadChip array. Downstream methylation analysis was performed in the R/Bioconductor package ChAMP. Gene ontology (GO) enrichment analysis on the methylation driven genes was done using PANTHER.</p><p>Results: mtDNA sequencing revealed that among the 6 cases of SEOC, there are 3 DP and 3 CR. Clustering analysis of differentially methylated CpGs (DMPs) between tumours of the same tissue type effectively distinguished endometrial and ovarian tumours into DP or CR. Thus, DP and CR endometrial tumour showed 50 DMPs and 15 differentially methylated regions (DMRs), but no significantly enriched signaling pathway was identified. On the other hand, there were 1,105 DMPs and 44 DMRs that mapped to 601 known genes between DP and CR ovarian tumours. GO analysis revealed that the hypomethylated genes in CR ovarian tumour were enriched in several metastatic-related processes, including cellular response to stimulus, regulation of cell projection organisation, cell migration and negative regulation of voltage-gated potassium channel activity.</p><p>Conclusions: Taken together, our findings demonstrated that DNA methylation profiling can be used for SEOC patient stratification and may enhance our understanding of epigenetic regulation of SEOC pathogenesis.</p>