Carbon-ion therapy spares surgery for early breast cancer

Chiba, Japan, January 22^nd 2026 — For many women with early breast cancer, surgery is effective but life-altering. New five-year data from the National Institutes for Quantum Science and Technology (QST) suggest that a precisely targeted, high-energy particle therapy may allow some patients to avoid surgery without compromising oncologic outcomes. In a single-center, prospective phase II study, carbon-ion radiotherapy provided durable tumor control with minimal side effects while preserving breast appearance in carefully selected patients who were unable or unwilling to undergo surgery. The study was published online on October 24, 2025, in the International Journal of Radiation Oncology*Biology*Physics.

The societal impact is clear: expanding access to a nonsurgical, organ-sparing treatment option has the potential to improve quality of life, particularly for older adults, patients with comorbidities, or those who wish to avoid mastectomy or lumpectomy. At five years, local control and disease-free survival rates were both 92%, overall survival was 100%, and no grade 2 or higher toxicities were observed. Most patients experienced only mild, transient skin reactions. Cosmetic outcomes were rated as “excellent” in all but one case, which later required mastectomy because of local recurrence.

“Carbon-ion radiotherapy combines high biological effectiveness with highly precise dose delivery,” said Noriyuki Okonogi, MD, PhD, QST Hospital. “In selected patients with small, estrogen receptor–positive, HER2-negative tumors, we observed complete responses in all cases, with sustained tumor control and minimal treatment-related burden.”

The research team treated twelve women aged 60 years or older with stage I invasive ductal carcinoma. Tumors were ≤2 cm in diameter. All patients received carbon-ion radiotherapy at a total dose of 60 Gy (RBE) delivered in four fractions over one week, followed by standard adjuvant aromatase inhibitor therapy for at least five years. Follow-up included serial MRI examinations until complete response—typically observed at around 12 months—followed by semiannual imaging thereafter. One in-field recurrence occurred in a tumor with a high Ki-67 index, underscoring the importance of biological factors in patient selection.

“The sharp dose conformity enabled by the Bragg peak allows us to spare healthy tissue while delivering ablative radiation to the tumor,” said Kumiko Karasawa, MD, PhD, QST Hospital. “The absence of clinically significant toxicity, together with preservation of breast appearance, is central to patients’ well-being and daily quality of life.”

Kazutoshi Murata, MD, PhD, Section Manager, Urinary and Reproductive Oncology Section, Department of Diagnostic Radiology and Radiation Oncology, QST Hospital, highlighted the broader implications:

“Our findings indicate that carbon-ion radiotherapy can provide a new treatment pathway for patients who value both oncologic safety and quality of life. As technology advances, we aim to expand access to this approach, thereby reducing the physical and emotional burden associated with surgery.”

This trial highlights how the unique physical and biological properties of particle therapy—namely high linear energy transfer and sharply confined dose deposition—can translate into tangible clinical benefits. Compared with photon-based ablative regimens, which have reported higher rates of moderate skin toxicity, carbon-ion therapy in this cohort achieved comparable tumor control with fewer adverse effects. The authors call for multi-institutional, controlled trials to validate these findings and to further refine biomarkers such as Ki-67 for optimal patient selection.

Looking ahead, the team envisions broader clinical availability within the next five years through expanded trials and dedicated treatment pathways for nonsurgical candidates. Over the next decade, carbon-ion radiotherapy protocols for breast cancer could be incorporated into standard treatment algorithms for well-defined patient subgroups—reducing surgical interventions while preserving body image and maintaining oncologic safety.

Reference

DOI: https://doi.org/10.1016/j.ijrobp.2025.10.020

About the National Institutes for Quantum Science and Technology, Japan

The National Institutes for Quantum Science and Technology (QST) was established in April 2016 to promote quantum science and technology in a comprehensive and integrated manner. The new organization was formed from the merger of the National Institute of Radiological Sciences (NIRS) with certain operations that were previously undertaken by the Japan Atomic Energy Agency (JAEA).

QST is committed to advancing quantum science and technology, creating world-leading research and development platforms, and exploring new fields, thereby achieving significant academic, social, and economic impacts.

Website: https://www.qst.go.jp/site/qst-english/

About Dr. Kazutoshi Murata

Dr. Kazutoshi Murata works at QST Hospital, National Institutes for Quantum Science and Technology (QST), Japan.

His research focuses on radiation oncology, particularly Gynecologic and Breast cancers, carbon-ion radiotherapy, and brachytherapy. He has published more than 60 papers in these fields, which have received more 1000 citations. His research covers topics such as carbon-ion radiotherapy for gynecologic and breast cancers, brachytherapy techniques and outcomes, and advanced radiation treatment planning.

Funding Information

This work was supported by JSPS KAKENHI grant number 25461935, 18K07772, 22K07729, 23K27560.