Abstract
PURPOSE: This study aimed to compare treatment outcomes between patients who received adjuvant radiotherapy (RT) and those who did not, in a cohort of patients with low-risk, early-stage breast cancer. MATERIALS AND METHODS: Postmenopausal women with pT1N0/Nx, grade 1-2, hormone receptor-positive, human epidermal growth factor 2-negative, and Ki-67 ≤ 20% breast cancer who underwent breast-conserving surgery and adjuvant endocrine therapy between 2010 and 2020 were included. The decision on RT omission was based on physician assessment and patient preference. The primary outcome was cumulative incidence of disease recurrence. Secondary outcomes included locoregional recurrence, overall survival, and breast cancer-specific survival. RESULTS: Of the 742 patients, 707 received adjuvant RT (postoperative radiation therapy [PORT] group) and 35 did not (RT omission group). Baseline characteristics were generally similar; however, the RT omission group was older (median age, 76 years; range, 68 to 85 years) than the PORT group (median age, 62 years; range, 55 to 87 years). After a median follow-up of 60 months in the PORT group and 52 months in the RT omission group, the 5-year cumulative incidence of disease recurrence was 1.28% and 0%, respectively (Gray's test, p = 0.305). Locoregional recurrence occurred in seven patients (1.0%) in the PORT group, whereas no locoregional recurrences were observed in the RT omission group. The results remained consistent after propensity score matching. CONCLUSION: Low-risk, early-stage breast cancer patients exhibited comparable disease recurrence and survival rates regardless of the RT status. Our study underscores the necessity for further investigation into RT omission in carefully selected patients.