Single-Cell Transcriptomic Profiling of Ectopic ACTH-Secreting Pheochromocytoma Reveals the Chromaffin Cell Origin of Ectopic Hormone Production.

Ectopic ACTH-secreting pheochromocytomas are rare and life-threatening endocrine tumors responsible for hypertension, paroxysmal symptoms, and Cushing's syndrome. The cellular origin of ACTH and the tumor's molecular characteristics remain poorly understood. Single-cell RNA sequencing was performed on tumor specimens and adjacent adrenal tissues from three patients with ectopic ACTH-secreting pheochromocytomas. Integrated bioinformatic analyses, including differential expression, functional enrichment, cell-cell communication, and pseudotemporal trajectory inference, were conducted. Key findings were supported by immunofluorescence and immunohistochemical staining. Our study integrated single-cell transcriptomic profiling with detailed clinical characterization of three cases of ectopic ACTH-secreting pheochromocytomas. All patients presented classic Cushing's features and variable catecholamine secretory patterns. Hormone levels improved after surgical resection. Single-cell analysis revealed a complex tumor microenvironment comprising 11 distinct cell populations. Chromaffin cells expressing the ACTH precursor gene POMC were identified within the tumor cell population, suggesting that these cells may represent the source of ectopic ACTH production. This finding was further supported by immunofluorescence and immunohistochemical staining demonstrating ACTH expression in CHGA-positive chromaffin tumor cells and absence of staining for the adrenocortical marker α-inhibin. These tumor cells exhibited metabolic reprogramming characterized by upregulation of oxidative phosphorylation pathways and downregulation of adaptive immune responses. Cell-cell communication analysis suggested interactions between POMC-expressing chromaffin cells and cytotoxic immune cells. Pseudotemporal trajectory analysis further suggested that these chromaffin cells did not transition toward a steroidogenic fate. This study provided a single-cell atlas of ectopic ACTH-secreting pheochromocytomas. Our integrated analysis suggested POMC-expressing chromaffin cells may represent the cellular source of ectopic ACTH production and revealed a transcriptional signature involving metabolic activation and immune modulation that might contribute to tumor progression. These findings offered new insights into the pathophysiology of this rare disease and provided a framework for future investigations into the molecular mechanisms underlying ectopic ACTH production.