Role of 10-Gy boost radiation after breast-conserving surgery for stage I-II breast cancer with a 5-mm negative margin

Background According to the Guidelines for breast-conserving therapy of the Japanese Breast Cancer Society, the surgical margin is "negative" when the minimum distance between the tumor edge and the margin of the resected specimen is more than 5mm. The value of boost radiation for early breast cancer with a 5-mm negative margin remains unclear. Methods. A total of 137 patients with stage I-II breast cancer underwent breast-conserving surgery between July 1987 and August 2002. All of the patients had negative margins according to the Japanese guidelines. Their median age was 50 years and the median follow-up period was 62 months. The entire ipsilateral breast was irradiated to a total dose of 50 Gy (25 fractions). Then an additional 10 Gy (5 fractions) was given to 79 patients, using 6- to 12-MeV electrons (boost group), while 58 patients (no-boost group) received no further radiation. Factors influencing local recurrence were evaluated by univariate and multivariate analyses. Results. For the entire population, the 5-year overall survival, cause-specific survival, disease-free survival, and local recurrence rates were 96.0%, 96.8%, 94.2%, and 1.67%, respectively. Boost radiation reduced local recurrence, but the improvement was not significant (P = 0.070). Univariate and multivariate analyses failed to detect any factors that were significantly associated with local control. There were no severe complications in either group and there were no differences between the groups in the cosmetic outcome. Conclusion. Boost radiation can be performed for stage I-II breast cancer with negative margins (Japanese guidelines), and showed a tendency to decrease local recurrence. A large randomized controlled study is necessary to establish final conclusions.