Tumor microenvironment remodeling across thyroid cancer differentiation states revealed by spatial transcriptomics.

[BACKGROUND] Thyroid cancer is the most common endocrine malignancy, with an increasing incidence, particularly driven by differentiated thyroid cancers (DTC), including papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC). Although DTC generally have excellent prognosis, dedifferentiated forms such as poorly differentiated thyroid cancer (PDTC) and anaplastic thyroid cancer (ATC) exhibit aggressive progression and poor outcomes. Understanding the tumor microenvironment (TME) is crucial for developing novel therapeutic strategies.

[METHODS] We performed spatial transcriptomics (ST) on formalin-fixed paraffin-embedded (FFPE) tumor tissues from 12 patients with PTC, FTC, PDTC, or ATC using the Visium CytAssist platform. Cell type composition was inferred using the CellDART algorithm, and pathway activity was assessed via PROGENy and REACTOME analyses. Immunohistochemical (IHC) assays were conducted to validate key TME components.

[RESULTS] ST analysis revealed significant shifts in cell composition associated with thyroid cancer dedifferentiation. Specifically, there was an increase in myeloid cells and cancer-associated fibroblasts (CAFs), accompanied by a reduction in natural killer (NK) cells and endothelial cells. Intratumoral heterogeneity in the Thyroid Differentiation Score (TDS) showed a strong spatial correlation with myeloid cell density, and among myeloid subtypes, the MDSC score was negatively correlated with TDS. Pathway activity analysis further identified upregulation of the JAK-STAT and VEGF signaling pathways in dedifferentiated tumors, both of which were closely associated with increased myeloid cell infiltration. IHC validation confirmed the differential expression patterns of representative immune and stromal markers across subtypes.

[CONCLUSIONS] These findings suggest that dedifferentiation in thyroid cancer is associated with an immunosuppressive TME that promotes tumor progression. Therapeutic strategies targeting JAK-STAT and VEGF pathways, or enhancing NK cell activity, may hold promises for aggressive thyroid cancers. Further studies with larger cohorts are necessary to validate these findings and develop targeted therapies for aggressive thyroid cancers.