The research, led by a team spanning Peking Union Medical College Hospital and Peking University First Hospital, applied single-cell RNA sequencing to fresh tumor specimens, comparing three ACTH- and CRH-secreting pheochromocytomas against three tumors that secreted neither hormone. The technique, which reads out the gene-expression profile of thousands of individual cells rather than averaging signals across a bulk tissue sample, allows researchers to disentangle the tumor cells themselves from the dense web of blood vessels, immune cells, and structural cells that surround them. That distinction matters, because modern cancer biology increasingly recognizes that a tumor is not a solitary mass of malignant cells but an ecosystem, and the character of that ecosystem can shape how a tumor behaves, spreads, and responds to treatment.

The first headline finding concerns the tumor cells’ internal identity. In the hormone-secreting tumors, the researchers detected markedly elevated expression of POMC, the pro-opiomelanocortin gene that serves as the raw blueprint for ACTH, alongside heightened CRH expression. This confirmed at the single-cell level that the ectopic hormone production is a genuine transcriptional program within the tumor cells, not an artifact of contamination by pituitary tissue or assay noise. In other words, these adrenal medullary tumors have switched on a genetic cassette that normally belongs to the hypothalamus and the anterior pituitary, effectively building a secondary hormonal control tower in the wrong part of the body.

Even more intriguing was the developmental state of those hormone-producing cells. Computational reconstruction of developmental trajectories, a method that arranges cells along a pseudotime axis reflecting their maturation, placed the hormone-secreting tumors in an earlier, more primitive state. The ACTH- and CRH-producing tumors were enriched for a population of cells resembling Schwann cell precursors, progenitor-like cells that in normal development give rise to the glial support cells of the peripheral nervous system. Their prominence at an early pseudotime position suggests that these tumors may retain, or revert to, a developmental plasticity that more mature, non-secreting pheochromocytomas lack. It is a hypothesis that fits a broader theme in neuroendocrine tumor biology: the most hormone-competent tumors are often the ones that refuse to fully grow up.

The team then asked which molecular puppeteers were pulling the strings. By constructing transcriptional regulatory networks, maps of which transcription factors are most active in driving gene expression within each cell population, they identified elevated activity of CEBPB, a transcription factor with well-established roles in inflammation, differentiation, and endocrine gene regulation, in the tumor cells of the hormone-secreting subtype. CEBPB’s heightened activity provides a candidate mechanistic link between the tumors’ primitive cell state and their ectopic hormonal output, and it now stands as a potential biomarker or therapeutic target for a disease so rare that dedicated clinical trials have been nearly impossible to mount.

But the study’s most visually striking results came from the tumor microenvironment. The hormone-secreting tumors were enriched for a distinctive population of endothelial cells, the cells that line blood vessels, marked by expression of SELE, the gene encoding E-selectin, an adhesion molecule that helps circulating immune cells dock onto vessel walls. Alongside these specialized vessels, the tumors harbored more CD8-positive T cells, the cytotoxic soldiers of the adaptive immune system. Communication analysis using the CellChat and NicheNet algorithms, which infer signaling conversations between cell types based on their complementary expression of ligands and receptors, showed that the hormone-producing tumor cells interacted more frequently with the SELE-positive endothelial cells, and predicted extracellular-matrix-associated crosstalk between those endothelial cells and the infiltrating T cells. The picture that emerges is of a tumor that has remodeled its own vasculature into an immune-permissive gateway, inviting cytotoxic lymphocytes into the tumor bed.

The non-secreting tumors told a nearly opposite story. They displayed stronger VEGFA-related angiogenic signaling, the classic vascular endothelial growth factor pathway that drives the construction of new, often disorganized blood vessels. Their microenvironments were richer in stromal populations, including cancer-associated fibroblasts, and in MRC1-positive macrophages of the M2-like variety, an immune cell type associated with immunosuppression, tissue remodeling, and tumor promotion rather than tumor killing. Signaling analysis revealed more prominent LGALS9-CD45 interactions between macrophages and T cells, a pathway implicated in dampening T cell activity. In short, the silent tumors appeared to build an immune-cold, pro-growth niche, while the hormone-secreting tumors built an immune-hot, vascularly distinctive one.

To guard against the pitfalls of a small sample, the researchers cross-validated their findings using data from The Cancer Genome Atlas and immunohistochemical staining of tumor tissue, grounding the single-cell discoveries in independent datasets and standard pathology. The convergence of these lines of evidence strengthens the case that the two pheochromocytoma subtypes differ not just in what hormones they release but in their fundamental cellular composition, developmental state, and immunological character. For a tumor type in which the hormonal phenotype is the clinical crux, the finding that the microenvironment diverges in parallel with hormone production suggests a deep coupling between a tumor’s endocrine behavior and its ecological architecture.

The clinical implications reach in several directions. Ectopic ACTH syndrome is a diagnostic nightmare: cortisol excess causes weight gain, hypertension, diabetes, muscle wasting, and profound vulnerability to infection, and locating the culprit tumor often requires an exhaustive hunt through the pituitary, lungs, pancreas, and adrenals. Understanding that ACTH- and CRH-secreting pheochromocytomas carry a specific molecular fingerprint, from POMC and CRH expression to CEBPB-driven regulatory programs and SCP-like cell states, could eventually sharpen the diagnostic toolkit and guide molecular profiling of tumors of unknown origin. The distinct immune landscapes also raise the possibility that the two subtypes might respond differently to immunotherapy or anti-angiogenic strategies, though the authors and the field alike caution that such applications remain speculative until tested in larger cohorts.

There are honest limits to keep in view. Six tumors, however deeply profiled, cannot capture the full heterogeneity of a disease this rare, and single-cell atlases describe correlations that must be confirmed functionally before they become causation. Yet the study exemplifies a broader transformation in how rare diseases are studied: instead of waiting decades to accumulate large cohorts, researchers can now extract dense mechanistic information from a handful of specimens and anchor it in public genomic resources. For patients whose tumors whisper in the wrong hormonal dialect, that shift may be the first step toward treatments designed not for the average pheochromocytoma, but for the specific, strange, and newly visible biology of their own.

Subject of Research: Single-cell transcriptomic profiling of ectopic ACTH/CRH-secreting pheochromocytomas

Article Title: Single-cell transcriptomic reveals transcriptional reprogramming and microenvironmental remodeling in ectopic ACTH/CRH-secreting pheochromocytomas

Article References: Su, W., Chen, S., Liu, J., Lian, P., Zhang, X., Zhang, Y., Han, W., Shen, Q., Zhang, D., Zhou, X., Xiao, Y., Ling, Q., Gao, Y., Lu, L., & Zhang, Z. (2026). Single-cell transcriptomic reveals transcriptional reprogramming and microenvironmental remodeling in ectopic ACTH/CRH-secreting pheochromocytomas. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09066-1

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09066-1

Keywords: pheochromocytoma, single-cell RNA sequencing, ectopic ACTH syndrome, Cushing's syndrome, tumor microenvironment, CEBPB, Schwann cell precursors, POMC, tumor immunology, adrenal medulla, angiogenesis, neuroendocrine tumors