Single-cell RNA-seq of small-intestinal neuroendocrine tumors reveals the cell of origin and gene expression of early tumor development.

Patients with a hereditary form of small-intestinal neuroendocrine tumors (SI-NETs) present with multiple synchronous tumors and precursors at various stages. Using this germline trait, single-cell RNA sequencing is performed to define the cell-of-origin and gene-expression trajectory in early tumor development. A subset of CES1(+), LCN15(-) enterochromaffin (EC) cells, residing at +4 position and below in the crypts, distinct from EC cells migrating up the villi, emerges as the putative SI-NET origin. PRODH2 is identified as a key biomarker for precursor cells, revealing stage-specific gene expression linked to early tumor development. From precursor to fully developed tumors, notable changes include the up-regulation of UCHL1 and MBD3L2, as well as the significant down-regulation of cell-cycle inhibitory genes, CDKN1A, CDKN1C, and CDKN2B, which play roles in cell survival and tumorigenesis. The current study provides insight into SI-NET initiation and progression, offering potential advancements in diagnosis, prevention, and treatment.