Clinical outcomes of boron neutron capture therapy for unresectable oral cancer: a retrospective analysis

Background: Surgery is the standard treatment for oral cancer but often causes functional and cosmetic problems, and reoperation is difficult. Radiotherapy (RT) is less effective, with reirradiation limited by normal tissue tolerance and salvage surgery after RT carrying high complication risks. Systemic therapy is used for local recurrence but yields poor outcomes, underscoring the need for better options. Boron neutron capture therapy (BNCT) is an established method that selectively delivers high tumor doses. This study evaluated BNCT efficacy and safety in unresectable oral cancers not amenable to definitive RT. Methods: This retrospective study included oral cancer patients treated with BNCT between June 2020 and June 2024 under the Japanese public health insurance system. Primary endpoints were best treatment response and incidence of adverse events (AEs), particularly severe oral mucositis (Grade ≥ 3 by Common Terminology Criteria for AEs version 5). Predictors of severe oral mucositis were also examined. Secondary endpoints included overall survival (OS), locoregional control (LRC), and progression free survival (PFS). Results: Among 74 patients (follow-up period ≥3 months), the majority (73%) had recurrent cancer. The complete response rate was 50%. The major severe acute AE was severe oral mucositis (all Grade 3) in 26% of patients. The maximum oral mucosal dose and the number of dental metals were significant predictors of severe oral mucositis. The 2-year OS, LRC, and PFS rates were 49%, 52%, and 29%, respectively. Conclusion: This study suggests that BNCT is an effective and safe treatment for unresectable oral cancers that cannot be definitively irradiated.