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.
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.
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.
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.
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.
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.
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.
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.
Authors
Okonogi Okonogi, Karasawa Karasawa, Murata Murata, Omatsu Omatsu, Murata Murata, Wakatsuki Wakatsuki, Ishikawa Ishikawa
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