The 9th Version of the AJCC Staging System for Nasopharyngeal Carcinoma: A Guide for Radiologists.

Version 9 of the AJCC staging system for nasopharyngeal carcinoma (NPC) introduces important refinements, emphasizing improved prognostic accuracy, clarity, and clinical relevance. Building on the 8th edition, it refines TNM classifications to address limitations in survival outcome stratification and incorporates new criteria. Specifically, version 9 clarifies the criteria for T3 disease by requiring unequivocal evidence of bone involvement-namely, involvement of the skull base (including the pterygoid plates), cervical vertebrae, or paranasal sinuses. It additionally introduces advanced radiologic extranodal extension as a criterion for the N3 category and subdivides M1 disease into M1a disease (three or fewer metastatic lesions) and M1b disease (more than three metastatic lesions) to enhance risk stratification. Developed through extensive multicenter studies and validated by international panels, version 9 redefines NPC stage groups, aligning clinical management with evidence-based practices and improving prognostic accuracy. This Review highlights the key modifications in version 9 that are relevant to radiologists, providing imaging examples and considering implications for clinical practice, prognosis, and treatment planning.