早期乳がんに対する切除を行わない重粒子線治療の有効性と有用性を確認～手術を希望しない早期乳がん患者の新たな治療選択肢として期待～

2026-01-05 量子科学技術研究開発機構

図1 『重粒子線治療後の長期的治療効果
5年全生存率は100%、5年局所制御率および無病生存率はいずれも92%でした。
(5年以降に1例遠隔転移再発をしている)

<関連情報>

• https://www.qst.go.jp/site/press/20260105.html
• https://www.redjournal.org/article/S0360-3016(25)06395-3/fulltext

早期乳がんに対する非外科的治療としての炭素イオン放射線療法:最初の前向き臨床試験の第2相試験の5年間の結果 Carbon-Ion Radiation Therapy as Nonsurgical Treatment for Early-Stage Breast Cancer: 5-Year Results From the Phase 2 Part of the First Prospective Clinical Trial

Noriyuki Okonogi, MD, PhD ∙ Kukimo Karasawa, MD, PhD ∙ Kazutoshi Murata, MD, PhD ∙ … ∙ Hiroto Murata, MD, PhD ∙ Masaru Wakatsuki, MD, PhD ∙ Hitoshi Ishikawa, MD, PhD
International Journal of Radiation Oncology, Biology, Physics  Published:October 24, 2025
DOI:https://doi.org/10.1016/j.ijrobp.2025.10.020

Abstract

Purpose

To evaluate the long-term efficacy, safety, and cosmetic outcomes of carbon-ion radiation therapy (C-ion RT) as a nonsurgical treatment option for patients with early-stage breast cancer.

Methods and Materials

This single-center, prospective phase 1/2 trial enrolled women aged ≥60 years with stage I (cT1N0M0), estrogen receptor-positive, human epidermal growth factor receptor type 2-negative invasive ductal carcinoma, ≤2 cm in diameter. Patients received C-ion RT at a total dose of 60 Gy (relative biological effectiveness) in 4 fractions, followed by adjuvant aromatase inhibitors. The primary endpoint was 5-year local control. Secondary endpoints included complete response (CR) rate, adverse events (AEs), cosmetic outcomes, disease-free survival, and overall survival. Imaging was used for evaluating tumor response, and follow-up was conducted for a median of 73 months.

Results

Twelve patients were treated in the phase 2 component of the trial. The CR rate was 100%, with a median time to CR of 12 months (range, 4-36 months). The 5-year local control and disease-free survival rates were both 92%, and the overall survival rate was 100%. One case of in-field recurrence occurred in a patient with a high Ki-67 index. Acute grade 1 dermatitis was observed in 6 patients. No grade ≥2 acute AEs were reported. Regarding late AEs, grade 1 rib fractures (n = 2) and grade 1 mastitis-related pain (n = 3) were managed conservatively. Magnetic resonance imaging revealed subclinical pectoral muscle inflammation in 7 cases. All patients except one (who underwent mastectomy due to recurrence) maintained excellent cosmetic outcomes.

Conclusions

C-ion RT demonstrated excellent long-term tumor control with minimal toxicity and favorable cosmetic outcomes in selected patients with early-stage breast cancer. These findings support its potential as a nonsurgical alternative for patients who are medically inoperable or decline surgery, warranting further investigation in larger, controlled trials.