Postmastectomy radiotherapy in high-risk breast cancer patients given adjuvant systemic therapy. A 30-year long-term report from the Danish breast cancer cooperative group DBCG 82bc trial

•We present a comprehensive analysis of the DBCG 82bc randomized trial with a 30-year long-term follow-up.•I am study with 3083 patients did we evaluate the importance of postmastectomy irradiation (PMRT) in high-risk pre- and postmenopausal breast cancer patients who also received adjuvant systemic therapy.•We observed that PMRT strongly improved the loco-regional tumor control and subsequent long-term survival.•Such benefit could be achieved without any excess ischemic heart damage or other non-breast cancer related death.•Thus, radiotherapy has an important role in the multidisciplinary treatment of breast cancer. Between 1982 and 1990 the Danish Breast Cancer Cooperative Group (DBCG) conducted a randomized trial in high-risk pre- and postmenopausal (