The transition from primary colorectal cancer to isolated peritoneal malignancy is associated with a hypermutant, hypermethylated state

This is the authors' abstract. We don't add key points for this paper.

Coloretcal Peritoneal metastases (CPM) develop in 15% of colorectal cancers. Cytoreductive surgery and heated intraperitoneal chemotherapy (CRS & HIPEC) is the current standard of care in selected patients with limited resectable CPM. Despite selection using known prognostic factors survival is varied and morbidity and mortality are relatively high. There is a need to improve patient selection and a paucity of research concerning the biology of isolated CPM. We aimed to determine the biology associated with transition from primary CRC to CPM and poor prognosis CPM, to identify those suitable for treatment with CRS & HIPEC and to identify targets for existing repurposed or novel treatment strategies. A cohort of patients with CPM treated with CRS & HIPEC was recruited and divided according to prognosis. Molecular profiling of the transcriptome, epigenome and genome of CPM and matched primary CRC was performed. CPM were characterised by frequent Wnt/ β catenin negative regulator mutations, mismatch repair mutations and resulting high tumour mutational burden and dysregulation of methylation suggested by frequent TET2 mutations and mutations suggesting an immune evasive phenotype. Several novel therapies could be targeted to these frequent mutations including porcupine inhibitors, immune checkpoint inhibitors and methylation inhibitors. Here we show the molecular features associated with CPM development and with poor prognosis. Potential applications include improving patient selection for treatment and in the development of novel and personalised treatments. NOVELTY AND IMPACT Colorectal peritoneal metastasis (CPM) are associated with limited and variable survival despite patient selection using known prognostic factors and optimal currently available treatments. There is a paucity of research concerning the biology of CPM. This study describes the biological landscape of CPM and the molecular features associated with CPM development, conferring poor prognosis and has identified that the majority of CPM develop a hypermutant phenotype that may be suitable for treatment with anti-PD1/CTLA4 immunotherapy.