Purpose: Since June 2020, boron neutron capture therapy (BNCT) has been a health care service covered by health insurance in Japan to treat locally advanced or recurrent unresectable head and neck cancers. Therefore, we aimed to assess the clinical outcomes of BNCT as a health insurance treatment and explore its role among the standard treatment modalities for head and neck cancers.Materials and Methods: We retrospectively analyzed data from patients who were treated using BNCT at Kansai BNCT Medical Center, Osaka Medical and Pharmaceutical University, between June 2020 and May 2022. We assessed objective response rates based on the Response Evaluation Criteria in Solid Tumors version 1.1, and adverse events based on the Common Terminology Criteria for Adverse Events, version 5.0. Additionally, we conducted a survival analysis and explored the factors that contributed to the treatment results.Results: Sixty‐nine patients (72 treatments) were included in the study, with a median observation period of 15 months. The objective response rate was 80.5%, and the 1‐year locoregional control, progression‐free survival, and overall survival rates were 57.1% (95% confidence interval [CI]: 43.9%–68.3%), 42.2% (95% CI: 30.1%–53.8%), and 75.4% (95% CI: 62.5%–84.5%), respectively. Locoregional control was significantly longer in patients with earlier TNM staging and no history of chemotherapy.Conclusions: BNCT may be an effective treatment option for locally advanced or recurrent unresectable head and neck cancers with no other definitive therapies. If definitive surgery or radiation therapy are not feasible, BNCT should be considered at early disease stages.

Background: This study was conducted to evaluate the real-world safety and efficacy of boron neutron capture therapy (BNCT) with borofalan(¹⁰B) in Japanese patients with locally advanced or locally recurrent head and neck cancer (LA/LR-HNC). Methods: This prospective, multicenter observational study was initiated in Japan in May 2020 and enrolled all patients who re-ceived borofalan(¹⁰B) as directed by regulatory authorities. Patient enrollment continued until at least 150 patients were enrolled, and adverse events attributable to drugs, treatment devices, and BNCT were evaluated. The patients with LA/LR-HNC were systematically evaluated to determine efficacy. Results: The 162 patients enrolled included 144 patients with squamous cell carcinoma of the head and neck (SCCHN), 17 patients with non-SCCHN (NSCCHN), and 1 patient with glioblastoma. Treatmentrelated adverse events (TRAEs) were hyperamylasemia (84.0%), stomatitis (51.2%), sialoadenitis (50.6%), and alopecia (49.4%) as acute TRAEs and dysphagia (4.5%), thirst (2.6%), and skin disorder (1.9%) as more common late TRAEs. One- and two-year OS rates in patients with recurrent SCCHN were 78.8% and 60.7%, respectively. Conclusions: This post-marketing surveillance confirmed the safety and efficacy of BNCT with borofalan(¹⁰B) in patients with LA/LR-HNC in a real-world setting.

As glioma stem cells are chemo- and radio-resistant, they could be the origins of recurrent malignant glioma. Boron neutron capture therapy (BNCT) is a tumor-selective particle radiation therapy. ¹⁰B(n,α)⁷Li capture reaction produces alpha particles whose short paths (5–9 µm) lead to selective killing of tumor cells. P-boronophenylalanine (BPA) is a chemical compound used in clinical trials for BNCT. Here, we used mass cytometry (Cytof) to investigate whether glioma stem-like cells (GSLCs) take up BPA or not. We used GSLCs, and cells differentiated from GSLCs (DCs) by fetal bovine serum. After exposure to BPA for 24 h at 25 ppm in 5% CO₂ incubator, we immune-stained them with twenty stem cell markers, anti-Ki-67, anti-BPA and anti-CD98 (heterodimer that forms the large BPA transporter) antibodies and analyzed them with Cytof. The percentage of BPA⁺ or CD98⁺ cells with stem cell markers (Oct3/4, Nestin, SOX2, Musashi-1, PDGFRα, Notch2, Nanog, STAT3 and C-myc, among others) was 2–4 times larger among GSLCs than among DCs. Analyses of in vivo orthotopic tumor also indicated that 100% of SOX2⁺ or Nestin⁺ GSLCs were BPA⁺, whereas only 36.9% of glial fibrillary acidic protein (GFAP)⁺ DCs were BPA⁺. Therefore, GSLCs may take up BPA and could be targeted by BNCT.