Challenging the Role of Subtotal Resection Following Proton Radiotherapy for Adenoid Cystic Carcinoma of the Head and Neck

Abstract

To report long-term outcomes of patients with adenoid cystic carcinoma (ACC) of the head and neck treated with proton radiotherapy. On this IRB-approved, single institutional prospective outcomes registry, 56 patients were included with de novo, nonmetastatic adenoid carcinoma of the head and neck treated with primary (n = 9) or adjuvant proton therapy from June 2007 to December 2021. The cohort had 30 women and 26 men with a median age of 57 years (range, 10-81 years). Twenty-nine percent (n = 16) had intracranial extension, 23% (n = 13) had orbital extension, and 55% (n = 31) had clinical cranial nerve involvement at the time of radiotherapy. Thirty patients underwent gross total resection (GTR), 26 had gross disease at the time of treatment undergoing a subtotal resection (STR) (n = 17) or biopsy alone (n = 9). The median dose to the primary site was 72.6 GyRBE (range, 64-74.4 GyRBE) delivered in either once (n = 19) or twice (n = 37) daily treatments. Thirty patients received either elective nodal irradiation (ENI) in a node negative neck or concurrent chemotherapy. With a median follow-up of 6.2 years (range, 0.9 - 14.7 years), the 5-year local-regional control (LRC), disease free survival (DFS), cause-specific survival (CCS) and overall survival (OS) were 88%, 85%, 89%, and 89%, respectively. Cranial extension (p = 0.003) and gross residual tumor (p = 0.0388) were factors associated with decreased LRC. While LRC for those with a GTR was 96%, those with STR or biopsy alone were 81% and 76%, respectively. T-stage (p = 0.0154), cranial extension (p = 0.0056), extent of resection (p = 0.0355), and gross residual tumor (p = 0.0094) were associated with decreased DFS. T-stage (p = 0.0099), extent of surgery (p = 0.029) and gross residual tumor (p.0071) were associated with decreased CCS. The 5-year cumulative incidence of clinically significant late grade ³3 toxicity was 15% and the crude incidence at most recent follow-up was 23% (n = 13). There was no LRC benefit with ENI (p = 0.94). Proton therapy provides excellent disease control for head and neck ACC with acceptable toxicity. Gross residual disease at the time of treatment and intracranial involvement were significant prognostic features for worse outcomes. STR did not confer benefit over biopsy only at 5-years and may question the role of extensive and morbid operations if GTR is not technically feasible.