(629) Impact of Time to Initiation of Postoperative Radiation Therapy on Survival in Adenoid Cystic Carcinoma

Introduction: Adenoid cystic carcinoma (ACC) of the salivary glands is a rare malignancy with high rates of perineural invasion and late recurrence. Current guidelines support postoperative radiotherapy (PORT) for resected ACC, but do not specify an optimal time to PORT (TTP). While timeliness of PORT is established in head and neck squamous cell carcinoma, analogous benchmarks are not well defined for salivary gland cancers. This gap is clinically important because care delays are potentially modifiable.

Methods: This multicenter, retrospective cohort study used the National Cancer Database to evaluate the association between overall survival (OS) and TTP. Inclusion criteria were patients diagnosed with primary salivary gland ACC from 2004 to 2023 who underwent definitive surgery and received PORT. Patients who had metastasis on presentation, neoadjuvant radiation therapy, and very late PORT (> 180 days) were excluded. Primary exposure was TTP at 5 weeks ( < 5 weeks vs ≥ 5 weeks). Multivariable Cox-proportional hazard model assessed independent association between TTP and OS, adjusting for age, sex, race, insurance status, zip-code median income, stage, treatment facility, and Charlson-Deyo comorbidity score. OS was estimated using Kaplan-Meier methods and compared with log-rank testing.

Results: Between 2004 and 2023, there were 2,674 patients who met study criteria (mean [sd] age, 57 [15] years; 1,034 [39%] male). Of these, 760 patients had TTP of < 5 weeks from surgery and 1,914 patients had TTP ≥ 5 weeks. Patients who initiated PORT after 5 weeks experienced significantly worse OS (TTP hazard ratio [HR], 1.26 [95% CI, 1.13 to 1.39]). In multivariable Cox regression, delayed TTP remained an independent adverse prognostic factor for OS after adjustment for clinicopathologic covariates.

Conclusions: In a national cohort of salivary gland ACC treated with surgery and adjuvant radiotherapy, initiating PORT within 5 weeks was associated with improved OS and remained independently prognostic in adjusted analyses. These findings suggest that earlier delivery of adjuvant radiation may lead to superior survival outcomes in ACC.