Exploratory evaluation of preoperative apparent diffusion coefficient as a candidate prognostic imaging marker in salivary gland carcinoma.

BACKGROUND: Salivary gland carcinoma (SGC) lacks reliable preoperative prognostic markers. This exploratory study evaluated whether volume-based apparent diffusion coefficient (ADC) parameters derived from preoperative diffusion-weighted magnetic resonance imaging (MRI) were associated with clinical outcomes in patients with SGC. METHODS: Sixty-five patients who underwent radical surgery for SGC between 2014 and 2024 were retrospectively reviewed; 55 had evaluable preoperative diffusion-weighted imaging (DWI) data for ADC analysis. Whole-tumor ADC values were derived using dedicated software with a threshold-based semi-automated workflow, and the median ADC and entropy were extracted. Disease-free survival (DFS), local control, and overall survival were analyzed using the Kaplan-Meier method. Associations between clinicopathological or imaging variables and outcomes were assessed using log-rank tests, Cox proportional hazards regression, and Spearman's correlation analysis. RESULTS: Advanced pathological stage, high-grade histology, preoperative facial nerve palsy, and low median ADC were associated with worse DFS in univariate analyses. The median ADC was negatively correlated with pathological grade. In the multivariable Cox proportional hazards model, median ADC remained associated with DFS; however, this finding should be interpreted cautiously because of the limited number of events and the wide confidence interval. Entropy showed no significant association with clinical outcomes. CONCLUSIONS: Preoperative volume-based median ADC was associated with DFS in this exploratory cohort of patients with SGC. The median ADC may represent a candidate prognostic imaging marker for preoperative risk assessment. Further validation in larger cohorts with standardized MRI protocols is required before clinical application.