Distribution pattern of metastatic lymph nodes in 870 cases of nasopharyngeal carcinoma: A clue for individualized elective prophylactic neck irradiation.

Abstract

e18049 Background: We aimed to explore a potential individualized elective prophylactic neck irradiation (iEPNI) to optimize the current strategy by investigating the distribution of metastatic lymph nodes (LNs) in nasopharyngeal carcinoma (NPC). Methods: Magnetic resonance imaging (MRI) and clinical data of 870 non-distant metastatic NPC patients admitted to the Hunan Cancer Hospital between January 2019 and December 2019 were reviewed. All patients were staged using the 8th TNM staging system, and the LNs location was assigned based on the 2013 guidelines. According to the distribution patterns of the LNs in NPC, the intra-regional lymphatic drainage levels were categorized into the following three stations: Station 1st of level VIIa and II; Station 2nd of level III and Va; and Station 3rd of level IV, Vb, and Vc. Other levels were defined as extra-regional areas. Results: The incidence of LNs metastasis was 822/870 (94.5%), including 198 cases of unilateral metastasis and 624 cases of bilateral metastasis. Among the 870 patients, the most frequently involved intra-regional lymphatic drainage was level IIb (87.1%), followed by level VIIa (80.0%), IIa (61.8%), Va (30.6%), IV (21.4%), Vb (8.9%), and Vc (1.1%). In the extra-regional areas, the detailed LNs distribution was: level Ia (0.2%), level Ib (7.7%), level VI (0.1%), level VIIb (5.6%), level VIII (5.5%), level IX (0.3%), and level X (0.2%). The rates of LNs metastasis in Station 1st, Station 2nd, and Station 3rd were 820/870 (94.3%), 532/870 (61.1%), and 199/870 (22.9%), respectively. Only 4 patients were considered to be skipping metastasis among the three stations (4/870, 0.5%). Additionally, in 203 patients with unilateral Station 1st LNs metastasis, there were 86 (42.4%) and 37 (18.2%) patients with ipsilateral Station 2nd and Station 3rd metastasis, respectively, and 3 (1.5%) and 1 (0.5%) patients with contralateral Station 2nd and Station 3rd LNs metastasis, respectively. Conclusions: LNs spread from Station 1st to Station 3rd successively with rare skipping metastasis. A potential iEPNI strategy of prophylactical neck irradiation to the ipsilateral latter node-negative station might be feasible, which is detailed as follows: irradiation to Station 1st in patients with no LNs metastasis, irradiation to Station 2nd in patients with only Station 1st metastasis, and irradiation to Station 3rd in patients with Station 2nd metastasis but without Station 3rd metastasis. Further prospective investigations are expected to validate the strategy.