Global proposal for the TNM staging system for poorly differentiated thyroid cancer

Poorly differentiated thyroid cancer (PDTC) lacks a dedicated staging system, requiring use of the TNM-8 for differentiated thyroid cancer despite its distinct biology. A cohort study using data from the International Aggressive Thyroid Cancer Collaborative Group (IATCCG) aimed to develop a PDTC-specific staging system. The study included surgically treated patients at 91 centers in 14 countries from January 1984 to January 2026 (n=1010). External validation was performed using patients from the US SEER database (n=170). The primary endpoint was overall survival. With M1 disease predefined as stage IVB, the schema for stages I-IVA in patients with M0 disease were redefined. The analysis found that level VII lymph node metastasis was associated with significantly worse survival than level VI or lateral neck metastases, prompting its upgrading as a new N1c category and the establishment of a dedicated PDTC staging system with clear prognostic discrimination. The authors conclude that this proposed PDTC-specific staging system provides improved prognostic stratification reflecting its different biology. These data provide a strong rationale for the potential inclusion of a stand-alone AJCC staging system for PDTC.