207 Mapping Cellular Origins and Developmental Trajectories of Pituitary Neuroendocrine Tumors

INTRODUCTION: The cellular origins of pituitary neuroendocrine tumors (PitNETs) are uncertain, positing that PitNETs may originate from differentiated neuroendocrine cells or adult pituitary stem cells. Understanding these origins is essential for developing targeted therapies aimed at tumor-initiating cells, thereby enhancing treatment efficacy. METHODS: We conducted single-nucleus sequencing on approximately half a million cells, creating the largest database to date. This included samples from two non-tumor postmortem adult pituitaries and 11 resected PitNETs, covering somatotrophic, hormonally active and silent corticotrophic (SCAs), lactotrophic, silent gonadotroph (SGA), and null cell (NCA) adenomas. RESULTS: We reconstructed a single-nuclei atlas of the normal adult human pituitary gland, identifying pituitary stem cells expressing previously known and novel transcription factors. Integrating stem and neuroendocrine nuclei (corticotroph, gonadotroph, lactotroph, thyrotroph, and somatotroph) from normal controls with tumor samples traced the development of PitNET subtypes, with copy number variation (CNV) analysis used to assess chromosomal instability. While most PitNET subtypes derived from their differentiated normal counterpart cells (SGAs from gonadotroph cells, prolactinomas from lactotroph cells, SCA/secreting corticotrophic adenomas from corticotroph cells) and had significant CNV changes, somatotroph and null cell adenomas had minimal CNV changes and arose from pituitary stem cells. While secreting corticotrophic adenomas and SCAs originated from mature corticotroph cells, secreting corticotrophic adenomas appeared earlier in developmental trajectory, representing a less mature state than SCAs. On gene expression analysis, secreting corticotrophic tumors upregulated genes associated with cell morphogenesis and development, suggesting a non-terminal transitional state. Lastly, we characterized key pseudotime genes for each tumor subtype. CONCLUSIONS: This study provides detailed insight into the cellular origins and developmental pathways of various PitNET subtypes, revealing that both stem and differentiated cells can contribute to tumorigenesis in a subtype-specific manner.