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

INTRODUCTION: 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 GNAS and/or KRAS. However, the involvement of global epigenetic alterations in PMPs has not been reported. METHODS: 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. RESULTS: 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 HOXD1 and TSPYL5 in the 15 PMPs. CONCLUSIONS: 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.

Comparative transcriptomic analyses reveal activation of the epithelial-mesenchymal transition program in non-metastasizing low grade pseudomyxoma peritonei.

Epithelial-mesenchymal transition (EMT), angiogenesis, cell adhesion and extracellular matrix (ECM) interaction are essential for colorectal cancer (CRC) metastasis. Low grade mucinous neoplasia of the appendix (LAMN) and its advanced state low grade pseudomyxoma peritonei (lgPMP) show local aggressiveness with very limited metastatic potential as opposed to CRC. To better understand the underlying processes that foster or impede metastatic spread, we compared LAMN, lgPMP, and CRC with respect to their molecular profile with subsequent pathway analysis. LAMN, lgPMP and (mucinous) CRC cases were subjected to transcriptomic analysis utilizing Poly(A) RNA sequencing. Successfully sequenced cases (LAMN n = 10, 77%, lgPMP n = 13, 100% and CRC n = 8, 100%) were investigated using bioinformatic and statistical tests (differential expression analysis, hierarchical clustering, principal component analysis and gene set enrichment analysis). We identified a gene signature of 28 genes distinguishing LAMN, lgPMP and CRC neoplasias. Ontology analyses revealed that multiple pathways including EMT, ECM interaction and angiogenesis are differentially regulated. Fifty-three significantly differentially regulated gene sets were identified between lgPMP and CRC followed by CRC vs. LAMN (n = 21) and lgPMP vs. LAMN (n = 16). Unexpectedly, a substantial enrichment of the EMT gene set was observed in lgPMP vs. LAMN (FDR=0.011) and CRC (FDR=0.004). Typical EMT markers were significantly upregulated (Vimentin, TWIST1, N-Cadherin) or downregulated (E-Cadherin) in lgPMP. However, MMP1 and MMP3 levels, associated with EMT, ECM and metastasis, were considerably higher in CRC. We show that the different tumor biological behaviour and metastatic spread pattern of midgut malignancies is reflected in a different gene expression profile. We revealed a strong activation of the EMT program in non-metastasizing lgPMP vs. CRC. Hence, although EMT is considered a key step in hematogenous spread, successful EMT does not necessarily lead to hematogenous dissemination. This emphasizes the need for further pathway analyses and forms the basis for mechanistic and therapy-targeting research.

Progress on immuno-microenvironment and immune-related therapies in patients with pseudomyxoma peritonei.

Pseudomyxoma peritonei (PMP) is an indolent malignant syndrome. The standard treatment for PMP is cytoreductive surgery combined with intraperitoneal hyperthermic chemotherapy (CRS + HIPEC). However, the high recurrence rate and latent clinical symptoms and signs are major obstacles to further improving clinical outcomes. Moreover, patients in advanced stages receive little benefit from CRS + HIPEC due to widespread intraperitoneal metastases. Another challenge in PMP treatment involves the progressive sclerosis of PMP cell-secreted mucus, which is often increased due to activating mutations in the gene coding for guanine nucleotide-binding protein alpha subunit (GNAS). Consequently, the development of other PMP therapies is urgently needed. Several immune-related therapies have shown promise, including the use of bacterium-derived non-specific immunogenic agents, radio-immunotherapeutic agents, and tumor cell-derived neoantigens, but a well-recognized immunotherapy has not been established. In this review the roles of GNAS mutations in the promotion of mucin secretion and disease development are discussed. In addition, the immunologic features of the PMP microenvironment and immune-associated treatments are discussed to summarize the current understanding of key features of the disease and to facilitate the development of immunotherapies.

Undetectable circulating tumor DNA confirms the inability of pseudomyxoma peritonei to systemic dissemination.

The study of circulating tumor DNA (ctDNA) plays a pivotal role in advancing precision oncology, providing valuable information for individualized patient care and contributing to the ongoing effort to improve cancer diagnosis, treatment, and management. However, its applicability in pseudomyxoma peritonei (PMP) remains unexplored. In this multicenter retrospective study involving 21 PMP patients, we investigated ctDNA presence in peripheral blood using three distinct methodologies. Despite mucinous tumor tissues exhibiting KRAS and GNAS mutations, ctDNA for these mutations was undetectable in blood samples. In this pilot study, circulating tumor DNA was not detected in blood when the tumor harbored mutations of known significance. In the future, a study with a larger sample size is needed to confirm these findings and to determine whether ctDNA could identify patients at risk for early recurrence and/or systemic metastases.