Impact of Tumor Site and Adjuvant Radiotherapy on Survival of Patients with Adenoid Cystic Carcinoma: A SEER Database Analysis

SIMPLE SUMMARY: Adenoid cystic carcinoma (ACC) is a rare but lethal salivary gland tumor, comprising less than 1% of head and neck neoplasms. It can affect several sites in the head and neck region, but the potential role of tumor site on survival and treatment response remains unclear and, to this day, the role that tumor location plays in treatment planning and survival has not been considered. We sought to address these knowledge gaps via analyses of the Surveillance, Epidemiology, and End Results (SEER) database. Our analysis identified that patients with submandibular gland adenoid cystic carcinomas, particularly those with late-stage disease, had worse survival compared to other sites and benefited the most from adjuvant radiotherapy. In contrast, early-stage and non-submandibular adenoid cystic carcinoma patients showed no survival benefit from adjuvant radiotherapy (aRT). These results underscore the role of tumor site on treatment response and survival of patients with head and neck ACC. ABSTRACT: Adenoid cystic carcinoma (ACC) is a rare salivary gland tumor, displaying aggressive behavior with frequent recurrence and metastasis. Little information exists regarding the impact of clinicopathological parameters and adjuvant radiotherapy (aRT) on ACC disease specific (DSS) and overall survival (OS). We extracted demographic, treatment, and survival information of 1439 patients with major or minor intraoral salivary gland ACC from the Surveillance, Epidemiology, and End Results (SEER) database. The associations between tumor characteristics and aRT with OS and DSS were estimated using hazard ratios (HR) and 95% confidence intervals (CI). Submandibular gland ACCs had the worst prognosis (adjusted DSS HR = 1.48; 95% CI = 0.99–2.20, compared to parotid), and this difference was more pronounced among patients with advanced-stage tumors (adjusted DSS HR = 1.93; 95% CI = 1.13–3.30). aRT was associated with increased overall survival only among stage III submandibular ACC patients (HR = 0.64; 95% CI = 0.42–0.98) and had no benefit in any other group. In conclusion, submandibular gland ACC carries a worse prognosis than other gland subsites and may benefit from aRT. The different outcomes between submandibular gland and other major or minor gland ACCs warrant further mechanistic investigation.