Expanding role of radiotherapy in adenoid cystic carcinoma of the tracheobronchial tree: a new horizon

Background: Primary adenoid cystic carcinomas (ACCs) of central trachea-bronchi system are rare and heterogeneous tumors. Definitive radiotherapy (RT) is the recommended treatment in surgically unresectable or incomplete resection or in the presence of severe comorbidities. Objective: To evaluate the clinical features and outcomes of patients with ACC of trachea-bronchi treated with radiotherapy. Methods: Retrospective medical records review was done in all patients with histologically confirmed ACC of trachea-bronchi between January 2010 and December 2019. Patient disease and treatment characteristics and toxicity data were analyzed. Overall survival (OS), local recurrence-free survival (LRFS), and distant metastasis-free survival (DMFS) were computed using Kaplan-Meier method (log-rank test). Results: Nineteen patients (10 women and 9 men) were included in this analysis with median age of 40 years (range, 14–70). Of these patients, 63.2% (n = 12) presented in stage IV disease. Twelve and three patients received definitive (median dose 67.8 Gy) and adjuvant (median dose 50 Gy) RT, respectively. The median follow-up was 42.5 months (range, 4–120); 15 patients were alive and 4 were dead at that time. Local recurrence or progression was observed in 52.6% and distant metastasis found in 47.3% of patients. The 5-year OS, LRFS, and DMFS for all patients were 81.2%, 52.8%, and 39.6%, respectively. Baseline lymph node involvement showed significant impact on OS (56.3% vs 100%, p = 0.011). Among patients receiving definitive RT, patients with higher RT dose (⩾66 Gy) had significantly better survival outcomes (5-year LRFS: 75% vs 16.7%, p = 0.013). Conclusion: Definitive RT is an exemplary treatment for unresectable disease. Higher dose is recommended to improve long-term outcomes.