An appendiceal cancer organoid biobank identifies phenotypic evolution and druggable dependencies of peritoneal carcinomatosis.

Peritoneal carcinomatosis (PC) is a common yet deadly manifestation of gastrointestinal cancers, with few effective treatments. To identify targetable determinants of peritoneal metastasis, we focused on appendiceal adenocarcinoma (AC), which metastasizes almost exclusively to the peritoneum. No stable preclinical models of AC exist, limiting drug discovery and representing an unmet clinical need. We establish a stable biobank of 16 long-term cultured AC patient-derived tumor organoids (PDTOs). We establish an organoid orthotopic intraperitoneal xenograft model that recapitulates diffuse PC and show that PC organoids retain increased metastatic capacity, decreased growth-factor dependency, and decreased sensitivity to standard-of-care chemotherapy relative to matched primary AC organoids. Single-cell profiling reveals dedifferentiation from differentiated states in primary AC into intestinal stem cell and fetal progenitor states in AC-PC, with upregulation of oncogenic signaling pathways. We identify KRASMULTI-ON inhibitor RMC-7977 and the Wnt-targeting tyrosine kinase inhibitor WNTinib as clinically actionable strategies to target AC-PC more effectively.