Cell of origin and expression profiles of pseudomyxoma peritonei derived from the appendix.

Pseudomyxoma peritonei (PMP) is a rare disease caused by mucin-producing tumors that develop most frequently from the appendix. The disease is characterized by the accumulation of mucin in the abdominal cavity. Although frequent mutations in the KRAS and GNAS genes have been reported in PMP, gene expression profiles of the tumors remain to be fully clarified because of its rarity and the difficulties in collecting pure cancerous cells scattered within the mucin. To disclose the molecular features of PMP cells, we performed RNA-seq analysis of ten PMPs and their matched non-tumorous colonic epithelium in combination with laser-microdissection. As a result, we identified a total of 32 differently expressed genes (DEGs) between the tumors and non-tumorous colonic epithelium. A cell-of-origin subtype analysis with the nearest template prediction algorithm corroborated that PMP tumor cells belonged to the goblet cell subtype, and tumorous cells of PMP appear to arise from goblet cells. Interestingly, over representation analysis (ORA) uncovered that the tumors were significantly associated with three ontology terms, namely epithelial mesenchymal transition (EMT), angiogenesis, and inflammatory response. Comparison of gene expression profiles between disseminated peritoneal adenomucinosis (DPAM) and peritoneal mucinous adenocarcinomas (PMCA) identified a total of 687 DEGs. Additional gene set enrichment analysis (GSEA) revealed that ontology terms "G2M checkpoint" and "E2F targets" were significantly enriched in PMCA supporting the view that PMCA has more aggressive properties than DPAM. These data may be useful to further understand the molecular characteristics of PMP.