Abstract
BACKGROUND: Adenoid cystic carcinoma (ACC) of the external auditory canal (EAC) is an extremely rare head and neck malignancy. The study aimed to investigate the long-term outcomes and late toxicity of postoperative radiotherapy (PORT) for patients with EAC ACC. METHODS: Between 2004 and 2021, 60 patients with EAC ACC were retrospectively analyzed. The overall survival (OS), local recurrence-free survival (LRFS), nodal recurrence-free survival (NRFS), and distant metastasis-free survival (DMFS) were calculated by the Kaplan-Meier method. RESULTS: With a median follow-up of 110.3 months, the 10-year OS, LRFS, NRFS, and DMFS rates were 84.2%, 79.5%, 96.2%, and 59.9% after PORT, respectively. Eleven patients (18.3%) experienced local failure, 2 (3.3%) had regional failure, and 23 (38.3%) had distant metastasis (DM). Multivariate analysis showed that the advanced T stage (T3-4) was an independent risk factor for OS (p = 0.019) and DMFS (p = 0.006). Late toxicities were assessed in 45 patients. Among them, 73.3% (33/45) of patients experienced grade 3-4 ipsilateral hearing loss after surgery. Furthermore, xerostomia (31.1%, 14/45) and radiation-related caries (26.7%, 12/45) were the most common late toxicities of radiotherapy-related. For clinical N0 (cN0) patients (n = 58), the ipsilateral elective neck irradiation (ENI) did not improve the OS (p = 0.929), NRFS (p = 0.317), or DMFS (p = 0.778) for the advanced patients (T3-4). CONCLUSIONS: Surgery plus PORT is associated with excellent long-term survival with tolerable late toxicity for EAC ACC patients. ENI of cN0 patients shows no survival benefit, which suggests that the omission of ENI is reasonable to reduce radiation-related toxicity.