Abstract
PURPOSE: To evaluate survival outcomes and prognostic factors in breast cancer patients with clinically positive internal mammary lymph nodes (cIMN+) after combined-modality therapy, and to identify indicators for internal mammary nodal boost irradiation. METHOD: Consecutive cIMN + patients between January 2010 and April 2023 were retrospectively reviewed. According to nodal response to neoadjuvant therapy (NAT), patients were divided into three groups: no IMN clinical complete response (cCR) (Group A), IMN cCR without ALN pathological complete response (pCR) (Group B), both IMN cCR and ALN pCR (Group C). RESULTS: Among 141 eligible patients (median follow-up 49.5 months), the 5-year rates for overall survival (OS) and recurrence-free survival (RFS) were 85.7 % and 76.7 %, respectively. Multivariable analysis confirmed ALN pCR and IMN cCR as independent favorable prognostic factors. Patients in group C exhibited superior 5-year OS (97.4 % vs. 88.9 % vs. 71.0 %, p = 0.007) and RFS (93.9 % vs. 71.8 % vs. 61.4 %, p < 0.001), along with the lowest rate of distant metastasis (5.8 % vs. 22.7 % vs. 33.3 %, p = 0.003) compared to Groups B and A. In Group A patients, higher cumulative radiation dose (≥60 Gy) to IMN significantly improved both 5-year OS (71.0 % vs. 93.5 %, p = 0.009) and 5-year RFS (33.3 % vs. 69.3 %, p = 0.031). CONCLUSION: The dual achievement of IMN cCR and ALN pCR after NAT predicts exceptional outcomes. For patients with persistent IMN involvement after NAT, IMN dose escalation to ≥60 Gy significantly improved OS and RFS. These findings support individualized radiotherapy strategies based on nodal response.