Study of failure pattern among high-risk breast cancer patients with or without postmastectomy radiotherapy in addition to adjuvant systemic therapy: long-term results from the Danish Breast Cancer Cooperative Group DBCG 82 b and c randomized studies.

Purpose: Postmastectomy radiotherapy (RT) in high-risk breast cancer patients can reduce locoregional recurrences (LRRs) and improve disease-free and overall survival. The aim of this analysis was to examine the overall disease recurrence pattern among patients randomly assigned to receive treatment with or without RT.
Patients and Methods: A long-term follow-up was performed among the 3,083 patients from the Danish Breast Cancer Cooperative Group 82 b and c trials, except in those already recorded with distant metastases (DM) or contralateral breast cancer (CBC). The end points were LRR, DM, and CBC, and the follow-up continued until DM, CBC, emigration, or death. Information was selected from medical records, general practitioners, and the National Causes of Death Registry. The median potential follow-up time was 18 years.
Results: The 18-year probability of any first breast cancer event was 73% and 59% (P < .001) after no RT and RT, respectively (relative risk [RR], 0.68; 95% CI, 0.63 to 0.75). The 18-year probability of LRR (with or without DM) was 49% and 14% (P < .001) after no RT and RT, respectively (RR, 0.23; 95% CI, 0.19 to 0.27). The 18-year probability of DM subsequent to LRR was 35% and 6% (P < .001) after no RT and RT, respectively (RR, 0.15; 95% CI, 0.11 to 0.20), whereas the probability of any DM was 64% and 53% (P < .001) after no RT versus RT, respectively (RR, 0.78; 95% CI, 0.71 to 0.86).
Conclusion: Postmastectomy RT changes the disease recurrence pattern in high-risk breast cancer patients; fewer patients have LRR as first site of recurrence, and overall fewer patients have DM.