Patient selection

A total of 490 patients who were newly diagnosed with stage I NPC were identified from an inpatient database at the Sun Yat-sen University Cancer Center (Guangzhou, China) from June 2007 to September 2017.

Our NPC research team, consisting of head and neck surgeons, radiation oncologists, medical oncologists, pathologists, radiologists, and nuclear medicine physicians, established the indication, relative contraindication, and absolute contraindication criteria for applying ENPG in the localized stage I NPC.

The indication criteria for ENPG were: (1) had a maximum diameter of the primary tumor ≤ 1.5 cm; (2) distance of the tumor margin to the internal carotid artery was ≥ 0.5 cm; (3) the minimal axial diameter in magnetic resonance imaging (MRI) was no more than 0.4 cm for retropharyngeal lymph nodes (RPLN) and 0.6 cm for cervical lymph node (CLN). Relative contraindications criteria for ENPG were: (1) exogenous tumor diameter > 1.5 cm but tumor basis ≤ 1.5 cm; (2) RPLN and CLN ranged 0.4–0.5 cm and 0.6–1.0 cm, respectively, for minimal diameter but was proved negative by ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography (PET/CT) or pathology. Absolute contraindications criteria for ENPG were: (1) tumor basis diameter > 1.5 cm, or occupied the entire nasopharyngeal cavity; (2) T2–T4 primary tumor, i.e. tumor involving to or beyond the pharyngobasilar fascia; (3) N1–N3 regional lymph node metastasis. i.e. LN with central necrosis or annular enhancement, or groups of two or more lymph nodes (the minimal diameter ≥ 8 mm for CLN), or minimal diameter ≥ 0.5 cm for RPLN, or minimal diameter ≥ 1.0 cm for CLN; (4) had distant metastasis, i.e. bone, liver, or lung metastasis; (5) was physiologically unsuitable for surgery.

In the present study, the inclusion and exclusion criteria for applying ENPG were as follows:

Inclusion criteria: (1) all patients were previously untreated, pathologically diagnosed with undifferentiated or differentiated, keratinizing or nonkeratinizing NPC; (2) staged as T1N0M0 classification; stage I according to the 8th edition staging system of the American Joint Committee on Cancer [AJCC], referring to primary tumors confined in the nasopharyngeal cavity, and the RPLN and CLN were no more than 0.5 cm and 1.0 cm respectively. Of note, the inclusion criteria also comprised of patients with relative contraindications. Exclusion criteria: (1) in accordance with the absolute contraindications criteria; (2) without intention to surgery.

All patients provided preoperative written informed consent. The study was approved by the ethical committee of Sun Yat-Sen University Cancer Center.