Comparison of Clinical Outcomes of Definitive and Postoperative Radiotherapy for Adenoid Cystic Carcinoma of the Head and Neck: Can Definitive Radiotherapy Be a Treatment Option?

Simple Summary: Adenoid cystic carcinoma of the head and neck is a rare malignant tumor; thus, it is difficult to establish an optimal treatment based on clinical trials with a large number of enrolled patients. Retrospective analyses of a small number of cases have revealed that the standard treatment is surgical resection followed by postoperative radiotherapy, while definitive radiotherapy is considered inadequate. Previous studies have used classical techniques for radiotherapy and did not evaluate the efficacy of current radiotherapy techniques, which may have underestimated the efficacy of definitive radiotherapy. We retrospectively analyzed 44 cases of adenoid cystic carcinoma of the head and neck treated with current radiotherapy techniques. Our results show that definitive radiotherapy is comparable to surgical resection followed by postoperative radiotherapy with respect to overall survival and local control. The results suggest that definitive radiotherapy can be an effective treatment option for adenoid cystic carcinoma of the head and neck. Background: The standard treatment for adenoid cystic carcinoma of the head and neck is surgical resection followed by postoperative radiotherapy (PORT). Currently, definitive radiotherapy (defRT) is considered an inadequate treatment; however, its data are based on studies using classical radiotherapy techniques. Therefore, the therapeutic effects of current radiotherapy techniques have not been adequately evaluated, and it may have underestimated the efficacy of defRT. Methods: We retrospectively analyzed 44 adenoid cystic carcinoma patients treated with radiotherapy based on modern treatment techniques from 1993 to 2017. Results: Twenty-four patients underwent PORT and 20 patients underwent defRT. The 5-year overall survival rates for patients treated with PORT and defRT were 85.3% and 79.7%, respectively. The 5-year local control rates were 82.5% and 83.1%, respectively. There were no statistically significant differences in the overall survival and local control of patients treated with PORT and defRT (p = 0.4392 and p = 0.0904, respectively). Conclusion: Our results show that defRT is comparable to surgical resection followed by PORT with respect to overall survival and local control. The results suggest that defRT can be an effective treatment option for adenoid cystic carcinoma of the head and neck.