Disruption of WNT/Notch signaling in pancreatic cancer reveals tumors depend on the intricate equilibrium of malignant cell states.

Control of cell identity and number is central to tissue function, yet principles governing the organization of malignant cells remain poorly understood. Using genetically engineered mouse models and orthotopic allografts with dual WNT reporter systems, we discover that pancreatic ductal adenocarcinoma (PDAC) organizes in a stereotypical pattern, whereby PDAC cells responding to WNT signals (WNT-R) neighbor WNT-secreting cancer cells (WNT-S). Lineage tracing reveals that the WNT-R state is transient and gives rise to a stable WNT-S state. A subset of WNT-S cells expressing DLL1 forms a functional niche for WNT-R cells. The genetic inactivation of WNT secretion or Notch pathway components, or the cytoablation of WNT-S cells, disrupts PDAC tissue organization, suppressing tumor growth and metastasis. Analysis of human PDAC tissues confirms conservation of these populations. PDAC growth depends on an intricately controlled equilibrium of functionally distinct cancer cell states, revealing the fundamental principles governing solid tumor organization and therapeutic opportunities.