Adenoid Cystic Carcinoma of the Skull Base: Retrospective National Cohort Analysis of Treatment Paradigms and Outcomes

Objectives: To examine a national cohort of patients with nasopharyngeal adenoid cystic carcinoma (ACC) for incidence, skull base invasion, overall survival, and treatment paradigms.

Design, Setting, and Participants: Retrospective national population-based study using Surveillance, Epidemiology, and End Results (SEER) program data of patients with ACC of the nasopharynx and skull base (NACC) between 2004 and 2016.

Main Outcomes and Measures: Primary outcomes included 5-year overall survival and locoregional control. Statistical analysis was performed using STATA 15.0 (STATACorp, College Station, Texas, United States). Spearman’s rank order correlation was used for ordinal, monotonic variables with p-values <0.05 considered statistically significant. Survival analysis was performed by Kaplan–Meier method, and comparison between groups was performed using log-rank test.

Results: Of the 2,385 cases of adenoid cystic carcinoma, 70 cases were classified as NACC. Twenty-one percent (15) involved invasion of the skull base or posterior pharyngeal wall, and 42% (30) were either stage 3 or stage 4. The 3- and 5-year overall survival rates were 73 and 61%, respectively. Zero percent had metastasis to the neck and 6 percent had metastasis to the lungs in the study population. Eighty percent of patients with advanced stage NACC received radiation therapy, while 35% of patients underwent surgery, and 35% received chemotherapy. Five-year survival was not significantly affected between the radiation and nonradiation treatment groups (p = 0.18). Histologic subtypes of adenoid cystic carcinoma were not assessed in this study.

Conclusion: NACC is rare in incidence and was most commonly treated with radiation therapy when advanced in stage, despite its general reputation as a radio-resistant tumor. Type of radiation therapy was not assessed in this study. Surgery can be useful in appropriately selected tumors. These results raise the possibility that nasopharyngeal ACC is a unique entity from ACC in other subsites and it may arise in a different genetic background. Long-term survival for NACC patients requires further study with the need for pathologic and genetic characterization to better stratify high- and low-risk subtypes of NACC.