Failure Patterns of Distant Metastasis after Intensity-Modulated Radiation Therapy in Patients with Nasopharyngeal Carcinoma

Abstract

This study aimed to explore factors associated with distant metastasis after intensity-modulated radiotherapy (IMRT) in patients with nasopharyngeal carcinoma (NPC), and to provide evidence that could be used to design new treatment strategies for NPC. We performed a retrospective analysis of 645 patients with NPC at three treatment centers in China, from January 2009 to December 2011. All patients had untreated, non-metastatic NPC prior to receiving IMRT. The Kaplan-Meier method was used to calculate patient survival rates, and log-rank testing was used to compare survival differences. Univariate analysis and Cox proportional hazard analysis were performed to explore treatment failure patterns and risk factors for distant metastasis after radiotherapy. Of the 645 patients, 17.5% (113/645) had distant metastasis 5 years after treatment. The median metastatic age was 47 years (range: 20-74 years), and the median metastatic time was 24 months after IMRT (range: 6-79 months). The 5-year overall survival rate (OS) was 84.2% and the 5-year recurrence-free survival (RFS) rate was 90.1%. The 1-year, 3-year, and 5-year distant metastasis-free survival (DMFS) rates were 96.6%, 87.4%, and 82.8%, respectively. Univariate and multivariate analysis showed that N staging, the size of the cervical lymph node, the presence of lower cervical lymph node metastasis, residual cervical lymph nodes at the end of radiotherapy, the residual cervical lymph node lesion size, and the time of cervical lymph node lesion complete remission were independent prognostic factors for DMFS (p<0.05). Radiotherapy combined with chemotherapy can reduce the incidence of distant metastasis after IMRT. The risk of distant metastasis after IMRT was positively correlated with N staging, lower cervical lymph node metastasis, the size of the cervical lymph nodes, residual NPC in cervical lymph nodes at the end of radiotherapy, and the residual cervical lymph node lesion size. Persistent residual cervical lymph node lesions three months after IMRT was a risk factor for poor prognosis, therefore more effective interventions should be explored.