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

Abstract

Background: An accurate staging system is crucial for cancer management. Evaluations for continual suitability and improvement are needed as staging and treatment methods evolve.

Methods: This was a retrospective study of 1609 patients with nasopharyngeal carcinoma investigated by magnetic resonance imaging, staged with the 7th edition of the American Joint Committee on Cancer (AJCC)/International Union Against Cancer (UICC) staging system, and irradiated by intensity-modulated radiotherapy at 2 centers in Hong Kong and mainland China.

Results: Among the patients without other T3/T4 involvement, there were no significant differences in overall survival (OS) between medial pterygoid muscle (MP) ± lateral pterygoid muscle (LP), prevertebral muscle, and parapharyngeal space involvement. Patients with extensive soft tissue involvement beyond the aforementioned structures had poor OS similar to that of patients with intracranial extension and/or cranial nerve palsy. Only 2% of the patients had lymph nodes > 6 cm above the supraclavicular fossa (SCF), and their outcomes resembled the outcomes of those with low extension. Replacing SCF with the lower neck (extension below the caudal border of the cricoid cartilage) did not affect the hazard distinction between different N categories. With the proposed T and N categories, there were no significant differences in outcome between T4N0-2 and T1-4N3 disease.

Conclusions: After a review by AJCC/UICC preparatory committees, the changes recommended for the 8th edition include changing MP/LP involvement from T4 to T2, adding prevertebral muscle involvement as T2, replacing SCF with the lower neck and merging this with a maximum nodal diameter > 6 cm as N3, and merging T4 and N3 as stage IVA criteria. These changes will lead not only to a better distinction of hazards between adjacent stages/categories but also to optimal balance in clinical practicability and global applicability.

Keywords: TNM staging system; nasopharyngeal cancer; prognostication.

Figure 1

Overall survival: (A) T2 subgroups (different adjacent soft tissue involvement), (B) T3 subgroups (pterygoid structures vs skull base erosion), and (C) T4 subgroups (extensive soft tissue involvement vs intracranial/cranial nerve involvement).

Figure 2

Differences in defining criteria between the current 7th edition and the proposed 8th edition: (A) changing the extent of soft tissue involvement as T2 and T4 criteria and (B) replacing the supraclavicular fossa (blue) with the lower neck (ie, below the caudal border of cricoid cartilage; red) as N3 criteria. CS indicates carotid space; LP, lateral pterygoid muscle; M, masseter muscle; MP, medial pterygoid muscle; PG, parotid gland; PPS, parapharyngeal space; PV, prevertebral muscle; T, temporalis muscle.

Figure 3

Prognostication by T category with (Left) the current 7th edition and (Right) the proposed 8th edition: (A) local failure-free rate, (B) distant failure-free rate, and (C) overall survival.

Figure 4

Prognostication by N category with (Left) the current 7th edition and (Right) the proposed 8th edition: (A) nodal failure-free rate, (B) distant failure-free rate, and (C) overall survival.

Figure 5

Prognostication by stage group with (Left) the current 7th edition and (Right) the proposed 8th edition: (A) locoregional failure-free rate, (B) distant failure-free rate, and (C) overall survival.