Systemic Therapeutic Options in Radioiodine-Refractory Differentiated Thyroid Cancer: Current Indications and Optimal Timing.

Thyroid cancer (TC) remains a prevalent malignancy, with over 820,000 global cases diagnosed in 2022. Differentiated thyroid carcinoma (DTC), primarily papillary and follicular types, accounts for most cases and has a favorable prognosis with total thyroidectomy and radioiodine (RAI) ablation. However, 5-15% of patients develop RAI-refractory (RAI-R) disease, leading to a significantly poorer outcome. For RAI-R patients, treatment decisions depend on disease progression. Active surveillance is suitable for indolent cases, while symptomatic or progressive disease requires systemic therapy. Multikinase inhibitors (MKIs) such as lenvatinib and sorafenib serve as first-line options, with cabozantinib recently approved for resistant cases. Additionally, novel targeted therapies, including RET and NTRK inhibitors, and immune checkpoint inhibitors, are under investigation, offering a personalized approach. A key challenge is determining the optimal timing for systemic therapy, balancing progression-free survival (PFS) benefits against MKI-related toxicities, which significantly impact quality of life (QoL). Molecular testing can identify actionable mutations, guiding therapy selection. Clinical guidelines (ATA, ESMO) recommend initiating treatment based on disease progression and patient condition, integrating strategies such as active surveillance, surgery, and radiotherapy when appropriate. Despite advances, systemic therapies carry significant adverse events (e.g., hypertension, fatigue, gastrointestinal toxicity), necessitating careful monitoring to prevent dose reductions or interruptions. A multidisciplinary approach is essential to optimize patient outcomes and maintain QoL. As targeted therapies continue to evolve, further research is needed to refine treatment sequencing and improve outcomes for RAI-R TC. This review synthesizes current evidence to guide clinical decision-making.