The role of perineural invasion on head and neck adenoid cystic carcinoma prognosis: a systematic review and meta-analysis

Objective We performed a systematic review to assess the prognostic value of perineural invasion (PNI) for patients with head and neck adenoid cystic carcinoma. Study Design A literature search of MEDLINE and EMBASE was used to identify relevant literature up to December 2015. The primary outcomes of interest were overall survival, disease-free survival, and locoregional control. Study information and hazard ratios (HRs) were extracted, and HRs were pooled using the Mantel-Haenszel fixed-effects model and the DerSimonian and Laird random-effects model according to heterogeneity. Results Twenty-two studies and 1332 patients were included in this study. The PNI ratio was 43.2%. PNI was at increasing risk for overall survival (HR = 2.98; 95% confidence interval [CI] 2.00-4.46), disease-free survival (HR = 1.88; 95% CI, 1.42-2.49), and locoregional control (HR = 2.15; 95% CI, 1.48-3.13) with statistical significance. Conclusions PNI is an independent factor for poor prognosis in patients with head and neck adenoid cystic carcinoma. Moreover, PNI poses a significantly higher threat to male patients and younger patients.