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Abstract
Purpose: Although postoperative radiotherapy (PORT) is demonstrably effective in local control of head and neck adenoid cystic carcinoma (HNACC), its application is controversial and the subset of patients who would benefit most from PORT is unknown. Herein, we analyzed the data of HNACC patients to clarify the role of PORT.

Methods: We retrospectively reviewed 187 patients with nonmetastatic HNACC who underwent surgical resection between 2005 and 2019. The study endpoints were locoregional failure-free survival (LRFFS), progression-free survival (PFS), and overall survival (OS). Subgroup analysis and recursive partitioning analysis (RPA) were performed to identify patients most likely to benefit from PORT.

Results: With a median follow-up of 84.7 months, the 5-year LRFFS, PFS, and OS were 70.0%, 52.6%, and 86.4%, respectively. Survival was significantly shorter in patients who experienced local failure than in those who did not (5-year OS: 88.1% vs. 80.5%, P = 0.001). The local failure rate was significantly lower in patients who underwent PORT (16.9% vs. 31.0%, P = 0.021), despite the high frequency of adverse factors. Especially, significant decreases in local failure and similar OS rates could be obtained after PORT among patients with positive margins, T2-4 stage disease, and minor salivary gland tumors. The RPA model for PFS categorized patients into four groups according to three prognostic factors (T-stage, location, and sex). The RPA model for LRFFS and OS suggested three groups based on two factors (T-stage, margin for LRFFS; T-stage, grade 3 for OS).

Conclusion: PORT could prevent dismal survival, while significantly reducing local failures in high-risk HNACC patients.

Affiliations

Seo Hee Choi 1 2, Andrew Jihoon Yang 1 3, Sun Och Yoon 4, Hye Ryun Kim 5, Min Hee Hong 5, Se-Heon Kim 6, Eun Chang Choi 6, Ki Chang Keum 2, Chang Geol Lee 7
1Department of Radiation Oncology, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Gyeonggi-Do, Korea.
2Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Seoul, Korea.
3Department of Inpatient Medicine, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Gyeonggi-Do, Korea.
4Department of Pathology, Yonsei University College of Medicine, Severance Hospital, Seoul, Korea.
5Division of Medical Oncology, Department of Internal Medicine, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.
6Department of Otorhinolaryngology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.
7Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Seoul, Korea. cglee1023@yuhs.ac.