Postmastectomy internal mammary nodal irradiation: A long-term outcome

Background and objective: The internal mammary lymph nodes (IMN) have been recognized as a potential site of regional breast cancer spread. The aim of this study was to evaluate the impact of internal mammary node radiotherapy (RT) to on clinical outcomes in breast cancer patients treated with mastectomy and postoperative radiation therapy.
Materials and methods: This cohort study included 588 patients with breast cancers located in the central and medial quadrants. IMN RT was applied to 320 patients and 268 patients did not receive it IMN RT. Inside the IMN RT group, 165 patients received external beam IMN irradiation (IMN-EB). Mastectomy combined with using Californium-252 neutron source implantation was applied to 155 patients (IMN-BT). Cox proportional hazards modeling was used to determine the influence of IMN RT on clinical outcome. Age, tumor size, lymph nodal status, adjuvant radiotherapy, chemotherapy and hormonal therapy were assessed.
Results: IMN-EB resulted in a significant improvement of distant metastasis-free survival, breast cancer-specific survival and overall survival (P = 0.033, P = 0.037 and P = 0.011, respectively). The IMN-EB radiotherapy has a significant impact on event-free survival (HR, 0.67; 95% CI, 0.46–0.91; P = 0.043) and breast cancer-specific survival (HR, 0.64; 95% CI, 45–0.91; P = 0.013) in patients with moderate-risk (stage T_1–2 N₁). There was no association between IMN RT and clinical outcomes of patients with high-risk disease (stage T_3–4 N_2–3) in any of the study end points.
Conclusions: The effects of IMN-EB radiotherapy on event-free survival and breast cancer- specific survival were benefit for women with moderate-risk breast cancer.