Proposal for the 8th edition of AJCC/UICC staging system for nasopharyngeal cancer in the era of intensity-modulated radiotherapy

Abstract

Objective An accurate staging system is crucial for cancer management. With the development of cancer staging systems and therapeutic methods, the applicability and improvement of staging systems should be evaluated constantly. Methods The clinical data of 1609 nasopharyngeal carcinoma patients without metastasis at initial diagnosis, who were admitted to two tumor centers in Hong Kong and Mainland China and received intensity-modulated radiotherapy (IMRT), were analyzed retrospectively based on the 7th edition of the American Joint Committee on Cancer (AJCC) or International Union Against Cancer (UICC) staging system, and all the patients underwent magnetic resonance imaging (MRI) before treatment. Results Among the T3/T4 patients without involvement of other anatomic structures, overall survival (OS) showed no significant differences between the patients with masticator space (medial pterygoid muscle and/or lateral pterygoid muscle) involvement, prevertebral muscle involvement, and parapharyngeal space involvement. The OS was similar between the patients with extensive soft tissue (soft tissues other than the structures mentioned above) involvement and those with intracranial involvement or cranial nerve involvement. Only 2% of the patients had lymph node metastasis>6 cm above the supraclavicular fossa (SCF), with an OS similar to that of the patients with lower cervical lymph node metastasis. Replacing SCF with the lower neck (below the caudal border of the cricoid cartilage) did not affect the risk difference between different N stages. With the proposed T and N staging systems, the OS showed no significant differences between T4N0-2 and T1-4N3 patients. Conclusions After a review by AJCC/UICC staging system preparatory committees, the changes recommended for the 8th edition include changing medial pterygoid muscle or lateral pterygoid muscle involvement from T4 to T2, adding prevertebral muscle involvement to T2 stage, replacing SCF with the lower neck and combining this with a maximum lymph node diameter of>6 cm as N3 stage, and integrating T4 and N3 as stage ⅠVA. These changes result in a better risk difference between adjacent stages and achieve the optimal balance between clinical practicability and global applicability. Key words: Nasopharyngeal neoplasms/radiotherapy; Prognosis; TNM staging system