Previous meta-analyses have shown that postoperative radiotherapy for lymph node-positive breast cancer reduces the risk of recurrence and death. However, it is uncertain whether only three positive lymph nodes are beneficial. The aim of this study was to evaluate the efficacy of radiotherapy after mastectomy and axillary lymph node dissection. A collaborative group of early breast cancer trialists from the University of Oxford studied this in depth and found that for breast cancer patients with one to three positive lymph nodes, radiation therapy after mastectomy and axillary lymph node dissection reduced recurrence and breast cancer mortality, even when systemic therapy was given. The results of the study were published in the latest online edition of the March 2014 issue of THE LANCET, a leading international journal. The researchers conducted a meta-analysis of data from 8,135 patients in 22 trials from 1964 to 1986 who underwent mastectomy and axillary lymph node dissection followed by radiation therapy to the chest wall and local lymph nodes or no postoperative radiation therapy. Recurrence regression was followed up to January 1, 2009, and mortality follow-up lasted a total of 10 years. The investigators also stratified the analysis according to trial, individual follow-up time, age at enrollment, and pathologic lymph node status. A total of 3786 patients had at least secondary level axillary lymph node dissection, and patients had at least 0, 1 to 3, 4 or more positive lymph nodes. All subjects enrolled in the trial were treated with radiotherapy to areas including the chest wall, supraclavicular region or axilla (both), or internal breast chain radiotherapy. The investigators found no significant effect of radiotherapy on local recurrence, total recurrence, or breast cancer mortality for the 700 patients who had axillary lymph node dissection without positive lymph nodes. The effect of postoperative radiotherapy on survival and recurrence at 10 years was found to reduce local recurrence, total recurrence, and breast cancer mortality in 1133 of all 1314 patients who received systemic therapy (cyclophosphamide, methotrexate, fluorouracil, or tamoxifen) in the trial. For the 1,772 patients who underwent axillary lymph node dissection and had at least four positive lymph nodes, radiation therapy reduced local recurrence, total recurrence, and breast cancer mortality. From the results of this study, radiation therapy after mastectomy and axillary lymph node dissection reduced recurrence and breast cancer mortality in breast cancer patients with one to three positive lymph nodes, even when systemic therapy was given. Today, for women at low risk of recurrence living in certain countries, the absolute benefit may be less, but the proportional benefit from more effective radiotherapy is greater.