Is the benefit of postmastectomy irradiation limited to patients with four or more positive nodes, as recommended in international consensus reports? A subgroup analysis of the DBCG 82 b and c randomized trials

Background and aim: Numerous consensus reports recommend that postmastectomy radiotherapy (RT) in addition to systemic therapy is indicated in high-risk patients with 4+ positive nodes, but not in patients with 1-3 positive nodes. A subgroup analysis of the DBCG 82 b and c trials was performed to evaluate the loco-regional recurrence rate and survival in relation to number of positive nodes. Materials and methods: In the DBCG 82 b and c trials 3083 pre- and postmenopausal high-risk women were randomized to postoperative RT in addition to adjuvant systemic therapy. Since many patients had relatively few lymph nodes removed (median 7), the present analysis was limited to 1152 node positive patients with 8 or more nodes removed. Results: The overall 15-year survival rate in the subgroup was 39% and 29% (p = 0.015) after RT and no RT, respectively. RT reduced the 15-year loco-regional failure rate from 51% to 10% (p < 0.001) in 4+ positive node patients and from 27% to 4% (p < 0.001) in patients with 1-3 positive nodes. Similarly, the 15-year survival benefit after RT was significantly improved in both patients with 1-3 positive nodes (57% vs 48%, p = 0.03) and in patients with 4+ positive nodes (21% vs 12%, p = 0.03). Conclusion: The survival benefit after postmastectomy RT was substantial and similar in patients with 1-3 and 4+ positive lymph nodes. Furthermore, it was not strictly associated with the risk of loco-regional recurrence, which was most pronounced in patients with 4+ positive nodes. The indication for RT seems therefore to be at least equally beneficial in patients with 1-3 positive nodes, and future consensus should be modified accordingly