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

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.

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.

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.

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.