A risk score model for the metastasis of level Ib lymph node based on the clinicopathological features of nasopharyngeal carcinoma in a large sample.

The aim of the present study was to develop a metastatic risk score model of neck level Ib lymph nodes in primary nasopharyngeal carcinoma (NPC) to guide the level Ib radiotherapy. There were a total of 1,557 patients enrolled in the study, and of these patients, 1,145 were included in the training set. Univariate χ2 analysis and multivariate logistic regression analyses were used to screen the independent risk factors to construct the risk score model. A total of 85 patients in the validating set underwent a pathology biopsy of level Ib lymph nodes to test the model. The remaining 327 patients from the prognostic-research set were used to evaluate the prognostic impact of level Ib irradiation in high- and low-risk groups. The independent risk factors in the model were carotid sheath involvement, the maximal diameter of the neck lymph nodes (≥20 mm) and the involvement of the level II/III/IV lymph nodes. The involvement of level IV was assigned score 2 and the other risk factors were assigned score 1. According to the total scores, the patients were divided into the low- (total score, 0-1; level Ib metastasis rate, 0.5%) and high-risk groups (total score, 2-4; level Ib metastasis rate, 8.5%). In the validating set, the metastatic rate of level Ib in 43 low-risk patients was 0%, and the rate was 31.0% (13/42) in 42 high-risk patients. In the prognostic-research set, the prognosis of 137 low-risk patients was not affected by level Ib irradiation. However, level Ib unirradiation was an independent prognostic factor for the locoregional recurrence in 190 high-risk patients. According to the data, the novel score model could help assess the metastatic risk of level Ib in primary NPC, and the radiotherapy on level Ib may impact the locoregional recurrence in high-risk patients.