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

Journal of Clinical Oncology, Vol 25, No 22 (August 1), 2007: pp. 3259-3265

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.  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.

The relative risk reduction was significant in all age groups. However, in relation to the higher absolute risk in younger age groups, the observed absolute risk reduction at 10 years seemed to be larger in the younger patients: reduced from 23.9% to 13.5% in those age ≤ 40 years, from 12.5% to 8.7% in the 41- to 50-year age group, from 7.8% to 4.9% in the 51- to 60-year age group, and from 7.3% to 3.8% in those older than 60 years.

Conclusion: After 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.