PURPOSE: Boron neutron capture therapy (BNCT) perform as a treatment option for locally advanced or recurrent unresectable head and neck cancers since June 2020 in Japan. The effect of BNCT on parotid carcinoma, which presents a variety of histologic types, remains unclear. The object of this study was to investigate the antitumor efficacy of BNCT against parotid gland carcinoma by focusing on LAT1, which is involved in the uptake of L-BPA, the boron compound used in BNCT. MATERIALS AND METHODS: We performed a retrospective review of 42 high-grade parotid gland carcinoma cases. We immunostained specimens using an anti-LAT1 monoclonal antibody to assess the LAT1 expression rate. We divided the patients into two groups: LAT1 expression rate below 10% (negative group) and 10% or higher (positive group), and performed a survival rate analysis. RESULTS: The study included 42 patients categorized by histological three type into mucoepidermoid carcinoma (MEC), salivary duct carcinoma (SDC), and adenoid cystic carcinoma (AdCC). The LAT1 expression rate in the 42 cases was 37.5%, and the rates for each histological type were: AdCC 15.0%
MEC 17.5%
and SDC 60.0%. The 5-year disease-free survival (DFS) rates were 46.8% in the positive group and 81.8% in the negative group (p = 0.17). CONCLUSIONS: The LAT1 expression rate was 37.5% in cases of high-grade parotid gland carcinoma, and SDC exhibited particularly high expression. From the perspective of LAT1 expression, our results indicated that L-BPA-based BNCT is likely to achieve therapeutic efficacy against parotid gland carcinoma.