Omission of postoperative radiotherapy after breast-conserving surgery in low-risk breast cancer

Abstract Background This prospective cohort study aimed to assess whether postoperative radiotherapy could safely be omitted in women ≥ 65 years with low-risk, estrogen receptor (ER)-positive T1N0 breast cancer treated with breast-conserving surgery and adjuvant endocrine therapy. Methods Eligible patients were women ≥ 65 years with unifocal, non-lobular, grade 1 or 2, ER-positive, pT1N0 breast cancer treated with breast-conserving surgery and endocrine therapy for five years. Patients were followed up with mammography at least annually for 10 years. The primary endpoint was local recurrence. Secondary endpoints were contralateral breast cancer, recurrence-free survival, and overall survival. Results The final study cohort included 601 patients with a median age of 71 years (range: 65 to 90 years) and a median tumor size of 11 mm (range: 3 to 20 mm). Median follow-up time was 119 months (interquartile range: 103 to 121 months). The cumulative incidence of local recurrence was 1.5% (95% confidence interval (CI): 0.8 to 2.8%) and 5.5% (95% CI: 3.8 to 7.6%) at 5 and 10 years, respectively. The cumulative incidence of contralateral breast cancer was 1.7% (95% CI: 0.9 to 3.0%) at 5 years and 4.5% (95% CI: 3.0 to 6.6%) at 10 years. The overall survival rate at 10 years was 83.1% (95% CI: 80.8 to 85.4%). In total, three patients (0.5%) died due to breast cancer. Conclusion Our results support the possibility to omit radiotherapy after breast-conserving surgery in a well-defined subgroup of women aged ≥ 65 years with low-risk, ER-positive, pT1N0 breast cancer receiving adjuvant endocrine therapy.