Second Place Tie Residents' Competition: Irradiation effect after mastectomy on breast cancer recurrence in patients presenting with locally advanced disease

Background: Current guidelines recommend postmastectomy irradiation (PMI) for patients with tumors >5 cm and/or ≥4 positive lymph nodes. This study evaluates the effect of PMI on recurrence and survival within tumor size and node status groups. Methods: Locoregional and distant recurrences and survival for different tumor and treatment characteristics were analyzed in 2,797 patients with invasive breast cancer treated with mastectomy. Results: Tumor size, positive nodes, extranodal extension, lymphatic/vascular invasion, estrogen receptor/progesterone negative, HER-2 positive, and high grade were associated with significantly increased recurrence. In patients with ≥4 positive nodes and patients with tumors >5 cm and positive nodes, PMI decreased local and distant recurrence (overall 53% vs 24%, P < .001) and increased disease-free survival (P < .001) but not overall survival. In patients with less disease, a benefit from PMI irradiation could not be identified. Conclusions: PMI is indicated for patients with ≥4 positive nodes or patients with tumors >5 cm and positive nodes.