Three-Week Post-Mastectomy Radiation Equal to Five-Week

New 10-year data from a major clinical trial show that three weeks of radiation after mastectomy provides the same cancer control as the standard five-week schedule for women with high-risk breast cancer.

The findings were presented at the American Society for Radiation Oncology (ASTRO) 2026 Annual Meeting. The phase 3 trial enrolled 820 patients, almost all diagnosed with stage 3 disease, who had already undergone mastectomy and completed chemotherapy. The research team randomized participants to receive either 25 daily treatments over five weeks or 15 slightly larger doses over three weeks. Both arms were treated to the chest wall and the lymph nodes situated above the collarbone, following identical radiation field guidelines.

According to the study protocol, the only variable between the two groups was the total number of treatment days, while all other aspects of care remained constant. The outcomes were evaluated according to the trial’s predefined statistical plan, and independent committees reviewed imaging and clinical records to confirm events.

After a median follow-up of 11.5 years, cancer recurrence in the treated area occurred in 12.0% of the three-week group compared with 10.3% in the five-week group. The 1.7-percentage-point difference did not reach statistical significance, indicating that the abbreviated schedule did not raise the risk of local recurrence. Earlier five-year results, published in The Lancet Oncology in 2019, had shown a similarly small gap of 9.6% versus 8.6%, reinforcing the consistency of the long-term findings.

Beyond local control, the trial reported disease-free survival at 10 years of 69.9% for the three-week cohort and 65.2% for the five-week cohort. Overall survival stood at 77.5% versus 72.9%. Although the shorter regimen yielded slightly higher survival percentages, the differences were not statistically meaningful. These results suggest that the abbreviated approach does not compromise long-term outcomes.

Safety monitoring captured a range of radiation-related side effects. The study found no increase in complications such as arm swelling (lymphedema), skin changes, shoulder mobility issues, heart disease, or rib fractures. The only notable disparity was a higher incidence of mild, symptom-free lung scarring in the three-week arm, observed in 20% of those patients compared with 12% in the five-week group.

Study Design and Follow-Up Duration

The trial data were shared at the American Society for Radiation Oncology’s 2026 meeting in Boston, where researchers detailed a median follow-up period of 11.5 years. This represents one of the longest tracking periods for studies evaluating shorter radiation courses after mastectomy. Of the 820 participants initially enrolled, 810 were analyzed—401 receiving three-week treatment and 409 undergoing the five-week standard.