Impact of a higher radiation dose on local control and survival in breast-conserving therapy of early breast cancer:: 10-year results of the randomized boost versus no boost EORTC 22881-10882 trial

Purpose To investigate the long-term impact of a boost radiation dose of 16 Gy on local control, fibrosis, and overall survival for patients with stage I and II breast cancer who underwent breast-conserving therapy. Patients and Methods A total of 5,318 patients with microscopically complete excision followed by whole-breast irradiation of 50 Gy were randomly assigned to receive either a boost dose of 16 Gy ( 2,661 patients) or no boost dose ( 2,657 patients), with a median follow-up of 10.8 years. Results The median age was 55 years. Local recurrence was reported as the first treatment failure in 278 patients with no boost versus 165 patients with boost; at 10 years, the cumulative incidence of local recurrence was 10.2% versus 6.2% for the no boost and the boost group, respectively ( P < .0001). The hazard ratio of local recurrence was 0.59 ( 0.46 to 0.76) in favor of the boost, with no statistically significant interaction per age group. The absolute risk reduction at 10 years per age group was the largest in patients <= 40 years of age: 23.9% to 13.5% ( P = .0014). As a result, the number of salvage mastectomies has been reduced by 41%. Severe fibrosis was statistically significantly increased ( P < .0001) in the boost group, with a 10-year rate of 4.4% versus 1.6% in the no boost group ( P < .0001). Survival at 10 years was 82% in both arms. Conclusion A fter a median follow-up period of 10.8 years, a boost dose of 16 Gy led to improved local control in all age groups, but no difference in survival.