Spatial Heterogeneity, Stromal Phenotypes, and Therapeutic Vulnerabilities in Colorectal Cancer Peritoneal Metastasis.

PURPOSE: Peritoneal metastases (PM) in colorectal cancer portend a poor prognosis. We sought to elucidate molecular features differentiating primary tumors (PT) from PMs and actionable targets facilitating transcoelomic dissemination and progression. EXPERIMENTAL DESIGN: We performed multiomic profiling of 227 samples from 136 patients, including 56 PTs and 120 synchronous PMs comprising 34 matched PT-PM pairs. Whole-exome and bulk RNA sequencing analyses were conducted to identify underlying genomic aberrations and transcriptomic differences between primary and peritoneal lesions. We spatially characterized the microenvironment of tumor-stroma compartments and studied the roles of stromal phenotypes in promulgating tumorigenesis. RESULTS: Whole-exome sequencing found that genomic alterations and clonality patterns between PTs and PMs remain broadly similar. Transcriptomic profiles, however, suggest a transition as tumors reach the peritoneum toward a more mesenchymal tumor profile and fibrotic tumor microenvironment. Applying spatial profiling, we identify a fibro-collagenous and immune-infiltrated stromal phenotype [stromal cluster (SC) 2] characterized by increased cancer-associated fibroblasts, memory B cells, M2 macrophages, and T-cell exhaustion. These findings were orthogonally validated by multiplex IHC. Patients with SC2 stroma had poorer survival and were characterized by high SERPINE-1 (PAI-1) expression. PMs in patients with SC2 stroma were associated with enriched oncogenic pathways such as TGF-β. PAI-1 inhibition of colorectal cancer PM cell lines with a novel biologic demonstrated reduced IL2-STAT5 and TGF-β pathways and cell death. CONCLUSIONS: Our findings unveil distinctive and actionable molecular signatures, offering deeper insights into the intricate cross-talk between tumor cells and stromal microenvironments enabling PM in colorectal cancer.