Background: Radiotherapy prevents local recurrence of breast cancer after breast-conserving surgery. We evaluated the effect of a supplementary dose of radiation to the tumor bed on the rates of local recurrence among patients who received radiotherapy after breast-conserving surgery for early breast cancer.
Methods: After lumpectomy and axillary dissection, patients with stage I or II breast cancer received 50 Gy of radiation to the whole breast in 2-Gy fractions over a five-week period. Patients with a microscopically complete excision were randomly assigned to receive either no further local treatment (2657 patients) or an additional localized dose of 16 Gy, usually given in eight fractions by means of an external electron beam (2661 patients).
Results: During a median follow-up period of 5.1 years, local recurrences were observed in 182 of the 2657 patients in the standard-treatment group and 109 of the 2661 patients in the additional-radiation group. The five-year actuarial rates of local recurrence were 7.3 percent (95 percent confidence interval, 6.8 to 7.6 percent) and 4.3 percent (95 percent confidence interval, 3.8 to 4.7 percent), respectively (P<0.001), yielding a hazard ratio for local recurrence of 0.59 (99 percent confidence interval, 0.43 to 0.81) associated with an additional dose. Patients 40 years old or younger benefited most; at five years, their rate of local recurrence was 19.5 percent with standard treatment and 10.2 percent with additional radiation (hazard ratio, 0.46 [99 percent confidence interval, 0.23 to 0.89]; P=0.002). At five years in the age group 41 to 50 years old, no differences were found in rates of metastasis or overall survival (which were 87 and 91 percent, respectively).
Conclusions: In patients with early breast cancer who undergo breast-conserving surgery and receive 50 Gy of radiation to the whole breast, an additional dose of 16 Gy of radiation to the tumor bed reduces the risk of local recurrence, especially in patients younger than 50 years of age.