BackgroundLymph node metastasis in the cervical region posterior to level V (PLV) can occurs in patients with nasopharyngeal carcinoma (NPC), but the significance of lymph node metastasis in this region and the delineation of the radiotherapy target area have not been reported. We aimed to explore the distribution pattern and prognosis of metastatic lymph nodes in the PLV region in patients with NPC.MethodsWe retrospectively studied 605 cases of NPC diagnosed by pathological detection from December 2011 to November 2017. The nodal distribution at each level was assessed in accordance with the Radiation Therapy Oncology Group (RTOG) guidelines proposed in 2013. The central points of the metastatic lymph nodes of the PLV region in the patients were recreated proportionally on the CT images of a standard patient with N0 NPC in reference to the normal anatomy of the PLV area. The correlation between the PLV region and the other levels, the nodal location, and the characteristics and prognosis of the PLV region were analyzed.ResultsLymph node metastasis occurred in 557 (92.06%) of 605 patients. There were 30 patients (4.95%) with lymph node metastasis in the PLV region. A total of 49 metastatic lymph nodes from the PLV region were counted, and the mean vertical distance of the central point of each lymph node from the anterior surface of the trapezius muscle was 14mm. Linear regression correlation analysis suggested that lymph node metastasis in the PLV region was associated with ipsilateral level IVa (P=0.018), level Va, level Vb, and level Vc lymph node metastasis (all P< 0.001). The 5-year OS, PFS, LRFS, and DMFS of 29 patients with lymph node metastasis in the PLV region were 41.6, 27.7, 89.1, and 47.3%, respectively. Multivariate analysis showed that lymph node metastasis in the PLV region was an independent prognostic factor for DMFS (P< 0.05).ConclusionNPC patients with lymph node metastasis in the PLV region had a poor prognosis and a high risk of distant metastasis. We recommend that the margin of the PLV region may be a new cervical lymph node segment for NPC.