Breast-conserving surgery or mastectomy followed by radiotherapy is commonly used in the treatment of early-stage breast cancer. There is growing interest in delivering postmastectomy radiotherapy with hypofractionated schedules to reduce cost and enable the treatment of more patients. However, the efficacy and safety of this approach has not yet been compared to that of conventional postmastectomy radiotherapy in a randomized study. In this randomized controlled non-inferiority study, 820 patients with breast cancer who had undergone mastectomy and had at least four positive lymph nodes, or had tumor stage of T3-4 disease, were assigned to receive conventional fractionated radiotherapy or hypofractionated radiotherapy. The primary outcome was locoregional recurrence, defined as disease recurrence in the ipsilateral chest wall or regional lymph nodes from the time of randomization to the end of follow-up. Conventional fractionated radiotherapy consisted of postmastectomy radiotherapy at 50 Gy in 25 fractions over 5 weeks, and hypofractionated radiotherapy consisted of postmastectomy radiotherapy at 43.5 Gy in 15 fractions over 3 weeks. Patients received either adjuvant (75% of patients) or neoadjuvant (25% of patients) standard chemotherapy. The median follow-up was 58.5 months (IQR 39.2 months to 81.8 months). Researchers found that hypofractionated radiotherapy was noninferior to conventional fractionated radiotherapy in the 5-year cumulative incidence of locoregional recurrence (8.3% vs. 8.1% respectively, HR 1.10, 90% CI 0.72 to 1.69, p<0.0001 for non-inferiority). There was no difference in overall survival (OS) or disease-free survival (DFS) between the groups (HR 1.13 for OS, 95% CI 0.78 to 1.62, p=0.526; HR 0.88 for DFS, 95% CI 0.67 to 1.16, p=0.429). Grade 3 acute skin toxicity was less frequent in the hypofractionated radiotherapy group than in the conventional fractionated radiotherapy group (3% vs. 8% respectively, p<0.0001). There were no other significant differences between groups in the incidence of acute or late toxicities. However, the median follow-up of 5 years in this study was insufficient to assess for all potential late toxicities. In summary, this study supports the use of hypofractionated postmastectomy radiotherapy over conventional mastectomy radiotherapy for patients with high-risk breast cancer however, longer follow-up is needed to monitor for potential late toxicities.
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