Prognosis Of Preliminarily Diagnosed Nasopharyngeal Carcinoma Parotid Lymph Node Metastasis:A Propensity Score Matching Study

Objective: This study aims to investigate clinical features, prognosis value, and N staging attribution of parotid lymph node(PLN) of preliminarily diagnosed nasopharyngeal carcinoma(NPC) treated with Intensity-modulated radiation therapy(IMRT).Materials and Methods: This retrospective study collected 1616 cases which were first diagnosed in our hospital from June 2010 to December 2011, pathologically confirmed by nasopharyngoscopy biopsy, with Magnetic Resonance Imaging(MRI) data, and no distant metastasis. All patients received IMRT as the primary treatment to analyse clinical features, prognosis in the 7th AJCC, and to explore N staging attribution of PLN in preliminary NPC.Results: In the 1616 cases of the whole group, the incidence rate of PLN metastasis was2.8%. Among the 45 patients, 25 patients(55.6%) had extracapsular invasion of ipsilateral adjacent lymph nodes(Retropharygeal node and level II nodes), and also 8patients(17.8%) had parotid invasion by the parapaharyngeal space, only 4 of the 45 patients were isolated PLN metastasis. PLN metastasis was significantly associated with the N stage(P=0.001) and clinical stage(P=0.003),not the T stage(P=0.243).Univariate analysis showed that overall survival(OS), progression-free survival(PFS), distant metastasis-free survival(DMFS) or regional recurrence-free survival(RRFS) were impacted by PLN metastasis(P=0.016,0.001,0.001,0.001,respectively). Multivariate COX regression analysis showed PLN metastasis was an independent prognosis factor for PFS(P = 0.039, HR = 1.641,95% CI = 1.025-2.628), DMFS( P = 0.023, HR =1.793,95% CI = 1.085-2.962) and RRFS(P = 0.004, HR = 3.124,95% CI = 1.449-6.737).Using propensity score matching(PSM) correction for confounding factors, it seemed that PLN metastasis was an independent prognosis factor for OS, PFS, DMFS and RRFS(P=0.006, 0.001, 0.003, 0.022,respectively). Meanwhile,compared with N stage survival curve, the OS, PFS curve of PLN metastasis were separated with N2 curve, but were not statistically significant(P = 0.227,P=0.051), and were crossed with N3 curves(P = 0.654, P=0.494); The DMFS, RRFS curve of PLN metastasis were obviously separated with N2 curve(P = 0.018, P = 0.005), but were still crossed with N3(P =0.527, P = 0.098).Conclusion: PLN metastasis in premilinary NPC had a low incidence. And PLN metastasis should be suspected, when patients had ipsilateral pharyngeal and level II lymph node metastasis, invasion of nasopharyngeal parapharyngeal space, and extracapsular invasion of adjacent lymph nodes. PLN metastasis was significantly associated with the N stage and clinical stage,not the T stage.PLN metastasis was an independent prognosis factor for OS, DMFS, RRFS and PFS. PLN metastasis had poor prognosis, should be treated like N3 and its status in the Staging of NPC needs further study.