Could extra radiation after mastectomy keep breast cancer from coming back?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Eastern Cooperative Oncology Group Performance Status Scale 0-2 * Histologically confirmed invasive breast cancer * Underwent total mastectomy/breast-conserving surgery and axillary dissection(10 or more axillary lymph nodes detected) and negative margins * Patients who had ≥4 positive axillary lymph nodes; or 1-3positive axillary lymph nodes and T3-4; or 1-3positive axillary lymph nodes and T1-2, and score≥3 based on the following high risk factors: age≤40 years(score 1), primary tumor in the inner quadrant (score 1), 2-3 positive axillary lymph nodes (score 1), positive vascular invasion (score 1), re-staged based on eighth Cancer Staging System staging system(IB-IIA score 1， IIB-IIIA score 2); or ypN+ after neoadjuvant chemotherapy * No supraclavicular or internal mammary nodes metastases based on images before system therapy * No distant metastases * Could tolerate radiotherapy * Treated with chemotherapy (anthracycline and/or taxane-based combined chemotherapy, ≥6 cycles) * Anticipated to receive endocrine therapy for 5 years if indicated * Anticipated to receive anti-HER2 therapy for 1 years if indicated * LVEF≥50% based on echocardiogram * Willing to follow up * Written,informed consent Exclusion Criteria: * Simultaneous bilateral breast cancer * Sentinel lymph node biopsy only without axillary dissection * Had received internal mammary node dissection * No imaging assessment of the internal mammary nodal before system therapy * One-stage breast reconstruction * Severe cardiac insufficiency; myocardial infarction or uncorrected unstable arrhythmia or uncorrected unstable angina in the last 3 months; pericardial disease * Had history of chest wall or supraclavicular radiotherapy * Had simultaneous or previous secondary malignancies, except for non-malignant melanoma skin cancer, papillary thyroid / follicular carcinoma, cervical carcinoma in situ, contralateral non-invasive breast cancer