Methods and Materials: A retrospective study was conducted on 1,372 T1–T2 node-positive breast cancer patients treated at L’Hôtel-Dieu de Québec Hospital between 1972 and 1997.
Results: Among the patients who did not receive regional radiotherapy, the percentage of involved nodes was significantly associated with axillary failure. Ten-year axillary control rates were 97 % and 91 % when the percentage of involved nodes was <50 % and ≥50 % , respectively (p = 0.007). In addition, regional radiotherapy is always significantly associated with a decrease in overall regional failure (axillary and/or supraclavicular), regardless of the percentage of involved nodes. However, regional radiotherapy reduced the axillary failure rate (2 % vs. 9 % , p = 0.007) only when more than a specific percentage of nodes was involved (≥40 % if N1–3 and ≥50 % if N>3 nodes).
Conclusions: The percentage of involved nodes should be taken into consideration in selecting patients for regional radiotherapy. Irradiation of the axilla should be reserved for patients with a specific ratio: >40 % involved nodes if N1–3 and ≥50 % involved nodes if N>3 nodes.