Cancer cells retrace a stepwise differentiation program during malignant progression

Pancreatic Neuroendocrine Tumors (PanNETs) comprise two molecular subtypes, relatively benign islet tumors (IT) and invasive, metastasis-like primary (MLP) tumors. Hitherto, the origin of aggressive MLP tumors has been obscure. Herein, using multi-omics approaches, we revealed that MLP tumors arise from IT via dedifferentiation following a reverse trajectory along the developmental pathway of islet β-cells, which results in the acquisition of a progenitor-like molecular phenotype. Functionally, the microRNA-181cd cluster induces the IT-to-MLP transition by suppressing expression of the Meis2 transcription factor, leading to upregulation of a developmental transcription factor, Hmgb3. Notably, the IT-to-MLP transition constitutes a distinct step of tumorigenesis and is separable from the classical proliferation-associated hallmark, temporally preceding accelerated proliferation of cancer cells. Furthermore, PanNET patients with elevated Hmgb3 expression and an MLP transcriptional signature are associated with higher-grade tumors and worse survival. Overall, our results unveil a new mechanism that modulates cancer cell plasticity to enable malignant progression.