Molecular Determinants of Thyroid Cancer Progression: Thyroid Hormone Signaling, the BRAF/MAPK Pathway, and Emerging...

Thyroid cancer is the most common malignancy of the endocrine system and represents a biologically heterogeneous disease driven by the interplay between endocrine regulation, oncogenic signaling pathways, and tumor microenvironment dynamics. Although most follicular cell-derived thyroid cancers follow an indolent clinical course, a subset progresses toward aggressive, therapy-refractory phenotypes, underscoring the need for refined molecular understanding and improved biomarkers. This review comprehensively examines the molecular determinants of thyroid cancer progression, with particular emphasis on Thyroid Hormone (TH) signaling, the Mitogen-Activated Protein Kinase (MAPK) and Phosphoinositide 3-Kinase (PI3K)/AKT pathways, and the emerging role of microRNAs (miRNAs). We discuss how oncogenic alterations, most notably the ^V600EBRAF mutation, act as central drivers of tumor initiation and aggressiveness by sustaining MAPK/ERK signaling, promoting dedifferentiation, metabolic reprogramming, immune evasion, and resistance to targeted therapies. The cooperative role of PI3K/AKT signaling in reinforcing survival, invasion, and treatment resistance is highlighted, emphasizing the network-level integration of oncogenic pathways rather than linear dependency on single drivers. In parallel, thyroid hormones exert context-dependent effects on tumor biology through both genomic actions mediated by nuclear thyroid hormone receptors and non-genomic mechanisms initiated at the integrin αvβ3 receptor, linking endocrine status to cancer progression and therapeutic response. Finally, we review the expanding evidence supporting miRNAs as critical regulators of thyroid carcinogenesis and as promising diagnostic, prognostic, and predictive biomarkers. The clinical validation of miRNA-based panels and circulating miRNAs offers new opportunities to improve preoperative risk stratification, reduce overtreatment, and guide personalized therapeutic strategies. Collectively, these insights support a multidimensional framework for understanding thyroid cancer progression and highlight future directions for precision oncology.