Multi‐institutional retrospective study of mucoepidermoid carcinoma treated with carbon‐ion radiotherapy

This study aimed to evaluate the clinical outcomes of patients with mucoepidermoid carcinomas in the head and neck treated with carbon‐ion radiotherapy. Data from 26 patients who underwent carbon‐ion radiotherapy in four facilities were analyzed in this multi‐institutional retrospective study: the Japan Carbon‐ion Radiation Oncology Study Group. The median follow‐up time was 34 months. One patient experienced local recurrence, and the 3‐year local control rate was 95%. One patient developed lymph node recurrence and five developed distant metastases. The 3‐year progression‐free survival rate was 73%. Five patients died, two of mucoepidermoid carcinoma and three of intercurrent disease. The 3‐year overall survival rate was 89%. Acute mucositis and dermatitis of grade 3 or higher were experienced by 19% and 8% of patients, respectively; these improved with conservative therapy. Late mucositis and osteonecrosis of jaw were observed in 12% and 23% of patients, respectively. The 3‐year cumulative rate of any late adverse event of grade 3 or higher was 14%. None of the patients died of the acute or late adverse events. Carbon‐ion radiotherapy was efficacious and safe for treating mucoepidermoid carcinoma in this multi‐institutional retrospective study (registration no. UMIN000024473). We are currently undertaking a prospective multicenter study. Carbon‐ion radiotherapy is expected to be a promising treatment for patients with inoperable salivary gland cancers. The clinical outcomes for mucoepidermoid carcinoma as a distinct salivary gland tumor entity have not been clarified due to its rarity. Therefore, we evaluated the efficacy and safety of carbon‐ion radiotherapy for mucoepidermoid carcinoma in a multi‐institutional retrospective study. We believe that our study makes a significant contribution to the literature because carbon‐ion radiotherapy was shown to be efficacious, with a 3‐year overall survival rate of 89%. Furthermore, carbon‐ion radiotherapy was safe, with the 3‐year cumulative rate of any late adverse event of grade 3 or higher of 14%. None of the patients died of the acute or late adverse events.