Immune evolution and therapeutic vulnerabilities in thyroid cancer: from inflammation to immune escape

Thyroid cancer exhibits substantial heterogeneity in its tumor immune microenvironment (TIME), which critically shapes disease progression and therapeutic responsiveness. While most differentiated thyroid cancers (DTCs) remain indolent, a subset evolves into radioiodine-refractory disease or progresses to poorly differentiated (PDTC) and anaplastic thyroid carcinoma (ATC), characterized by aggressive behavior and limited treatment options. Emerging evidence suggests that this transition is accompanied by dynamic immune reprogramming rather than static immune evasion. In this review, we propose a stepwise model of immune evolution in thyroid cancer, spanning from autoimmune-driven inflammation in chronic lymphocytic thyroiditis (CLT) to immune-exhausted states in advanced tumors. We systematically characterize immune cell composition, functional states, and regulatory networks across disease stages, highlighting key shifts in antigen presentation, T-cell functionality, and myeloid cell polarization. Building on this framework, we integrate tumor immune phenotypes ("hot", "altered", and "cold") with actionable biomarkers, including PD-L1 expression, tumor mutational burden, IFN-γ signatures, M2 macrophage-related signature, and tertiary lymphoid structures. We further map these immune contexts to rational therapeutic strategies, encompassing immune checkpoint blockade, combination regimens with tyrosine kinase inhibitors or radiotherapy, and emerging approaches such as innate immune activation and adoptive cell therapies. By linking immune evolution with therapeutic vulnerabilities, this review provides a translationally relevant framework for precision immunotherapy in thyroid cancer and highlights future directions for overcoming resistance in advanced disease.