Non‑surgical breast‑conserving treatment using Kochi oxydol‑radiation therapy for unresectable carcinomas II for patients with stage 0 to IIIC breast cancer

Kochi Oxydol-Radiation Therapy for Unresectable Carcinomas (KORTUC) is a novel radiosensitizing treatment developed in Japan that involves intratumoral injections of hydrogen peroxide (H₂O₂) and sodium hyaluronate (HA). KORTUC II, an evolved form of the therapy, aims to enhance radiotherapy efficacy by locally increasing oxygen tension and inhibiting antioxidant enzymes in the tumor microenvironment. This study retrospectively evaluated the safety and efficacy of KORTUC-based breast-conserving therapy (KORTUC-BCT) in patients with stage 0-IIIC primary breast cancer who refused standard treatment protocols. A total of 50 patients who underwent KORTUC-BCT between February 2013 and April 2022 and had at least 1 year of follow-up were included. Radiotherapy consisted of short-course tangential irradiation at a dose of 44 Gy in 16 fractions. For patients with lymph node metastases, the supraclavicular region was included in the radiation field. A boost dose of 9-12 Gy was subsequently delivered to the tumor using electron-beam radiation therapy. The H₂O₂/HA sensitizer was intratumorally injected twice weekly under ultrasound guidance. All patients achieved a clinical complete response within a median evaluation time of 12 months. The 3-year local control rate for all cases was 89.3%; by stage, it was 100% for 0-I, 100% for IIA, 53.3% for IIB, 75% for IIIA, 75.0% for IIIB and 100% for stage IIIC. The 3-year disease-free survival rate was 75% overall; by stage, it was 100% for 0-I, 91.7% for IIA, 53.3% for IIB, 60.0% for IIIA, 75.0% for IIIB and 20.0% for IIIC. Lymph node metastasis sites had a 100% 3-year control rate. No grade ≥3 adverse events or cosmetic complications were observed. These findings suggest that KORTUC-BCT is a minimally invasive and well-tolerated therapy with promising outcomes, particularly for patients with early-stage breast cancer who decline surgery. This clinical study was registered in the UMIN clinical trials registry (UMIN000003734; June 10, 2010).