Prognostic influence of prevertebral space involvement in nasopharyngeal carcinoma: A retrospective study

•Nasopharyngeal carcinoma (NPC) may easily invade the prevertebral space.•Prevertebral space involvement (PSI) predicts poor prognosis in NPC.•Prognosis is particularly poor when tumor spread extends behind prevertebral muscle.•It might be reasonable to classify patients with PSI as T4 stage. To evaluate how prevertebral space involvement (PSI) and degree of tumor extension within the space affects prognosis in nasopharyngeal carcinoma (NPC). Data of patients with newly-diagnosed nonmetastatic NPC (n = 757) were retrospectively analyzed. Patients were separated into groups according to presence or absence of PSI and degree of tumor spread. Overall survival (OS), failure-free survival (FFS), local relapse–free survival (LRFS), and distant metastasis–free survival (DMFS) were compared between the groups. Prevalence of PSI, simple prevertebral muscle involvement (PMI), and behind prevertebral muscle involvement (BPMI) were 44.9% (340/757), 22.5% (170/757), and 22.5% (170/757), respectively. OS, FFS, LRFS, and DMFS for patients with and without PSI were 64% vs. 84.8%, 68% vs. 85.6%, 85.8% vs. 94.4%, and 78.5% vs. 92.8%, respectively (all P