Irradiation after mastectomy can reduce locoregional recurrences in women with breast cancer, but whether it prolongs survival remains controversial. We conducted a randomized trial of radiotherapy after mastectomy in high-risk premenopausal women, all of whom also received adjuvant systemic chemotherapy with cyclophosphamide, methotrexate, and fluorouracil (CMF).

A total of 1708 women who had undergone mastectomy for pathological stage II or III breast cancer were randomly assigned to receive eight cycles of CMF plus irradiation of the chest wall and regional lymph nodes (852 women) or nine cycles of CMF alone (856 women). The median length of follow-up was 114 months. The end points were locoregional recurrence, distant metastases, disease-free survival, and overall survival.

The frequency of locoregional recurrence alone or with distant metastases was 9 percent among the women who received radiotherapy plus CMF and 32 percent among those who received CMF alone (P<0.001). The probability of survival free of disease after 10 years was 48 percent among the women assigned to radiotherapy plus CMF and 34 percent among those treated only with CMF (P<0.001). Overall survival at 10 years was 54 percent among those given radiotherapy and CMF and 45 percent among those who received CMF alone (P<0.001). Multivariate analysis demonstrated that irradiation after mastectomy significantly improved disease-free survival and overall survival, irrespective of tumor size, the number of positive nodes, or the histopathological grade.

The addition of postoperative irradiation to mastectomy and adjuvant chemotherapy reduces locoregional recurrences and prolongs survival in high-risk premenopausal women with breast cancer.