Survival Impact of Adjuvant Therapy in Salivary Gland Cancers following Resection and Neck Dissection.

To evaluate the impact of postoperative radiotherapy (PORT) and chemotherapy on survival in salivary gland cancer (SGC) treated with curative-intent local resection and neck dissection. Retrospective population-based cohort study. National Cancer Database. Patients with SGC who were undergoing surgery were identified from the National Cancer Database between 2004 and 2013. Neck dissection removing a minimum of 10 lymph nodes was required. Because PORT violated the proportional hazards assumption, this variable was treated as a time-dependent covariate. Overall, 4145 cases met inclusion criteria (median follow-up, 54 months). PORT was associated with improved overall survival in multivariable analysis, both ≤9 months from diagnosis (hazard ratio [HR], 0.26; 95% CI, 0.20-0.34; P < .001) and >9 months (HR, 0.75; 95% CI, 0.66-0.86; P < .001). In propensity score-matched cohorts, 5-year overall survival was 67.1% and 60.6% with PORT and observation, respectively ( P < .001). Similar results were observed in landmark analysis of patients surviving at least 6 months following diagnosis. Adjuvant chemotherapy was not associated with improved survival (HR, 1.15; 95% CI, 0.99-1.34; P = .06). PORT, but not chemotherapy, is associated with improved survival among patients with SGC for whom neck dissection was deemed necessary. These results are not applicable to low-risk SGCs not requiring neck dissection.