Genome-Wide Analysis of DNA Methylation in Pseudomyxoma Peritonei Originated from Appendiceal Neoplasms

<b><i>Introduction:</i></b> Pseudomyxoma peritonei (PMP) is a disease characterized by progressive accumulation of intraperitoneal mucinous ascites produced by neoplasms in the abdominal cavity. Since the prognosis of patients with PMP remains unsatisfactory, the development of effective therapeutic drug(s) is a matter of pressing concern. Genetic analyses of PMP have clarified the frequent activation of <i>GNAS</i> and/or <i>KRAS</i>. However, the involvement of global epigenetic alterations in PMPs has not been reported. <b><i>Methods:</i></b> To clarify the genetic background of the 15 PMP tumors, we performed genetic analysis using AmpliSeq Cancer HotSpot Panel v2. We further investigated global DNA methylation in the 15 tumors and eight noncancerous colonic epithelial tissues using MethylationEPIC array BeadChip (Infinium 850k) containing a total of 865,918 probes. <b><i>Results:</i></b> This is the first report of comprehensive DNA methylation profiles of PMPs in the world. We clarified that the 15 PMPs could be classified into at least two epigenotypes, unique methylation epigenotype (UME) and normal-like methylation epigenotype (NLME), and that genes associated with neuronal development and synaptic signaling may be involved in the development of PMPs. In addition, we identified a set of hypermethylation marker genes such as <i>HOXD1</i> and <i>TSPYL5</i> in the 15 PMPs. <b><i>Conclusions:</i></b> These findings may help the understanding of the molecular mechanism(s) of PMP and contribute to the development of therapeutic strategies for this life-threatening disease.