Radiotherapy Field Approaches and Outcomes After Sentinel Lymph Node Biopsy and Axillary Lymph Node Dissection in Pathologic N1 Breast Cancer.

PURPOSE: To evaluate regional control and lymphedema according to radiotherapy field in patients with clinically node-negative (cN0) breast cancer who were diagnosed with pathological N1 (pN1) disease after breast-conserving surgery (BCS) and sentinel lymph node biopsy (SNB), using patients who underwent axillary lymph node dissection (ALND) as the comparison group.

METHODS

We retrospectively analyzed 616 patients with cN0/pN1 breast cancer who underwent BCS and received adjuvant radiotherapy between 2012 and 2018. Patients were classified into the SNB (n = 316) or ALND (n = 300) groups according to the axillary surgical procedure performed. Patients received standard-tangent radiotherapy, high-tangent radiotherapy, or comprehensive regional nodal irradiation at the treating physician's discretion. The primary endpoint was regional recurrence-free survival (RRFS), and secondary endpoints included overall survival (OS), disease-free survival (DFS), and breast cancer-related lymphedema (BCRL).

RESULTS

At a median follow-up of 91 months, the SNB and ALND groups did not differ significantly in terms of 10-year RRFS (98.5% vs. 95.4%; p = 0.109), OS (98.4% vs. 96.3%; p = 0.233), or DFS (92.3% vs. 91.6%; p = 0.566). BCRL was substantially more frequent in the ALND group than in the SNB group, both overall (32.7% vs. 10.1%; p < 0.001) and when defined as ≥ 2 cm (13.0% vs. 1.3%; p < 0.001). Within the SNB group, BCRL incidence did not differ significantly according to the radiotherapy field (p = 0.404).

CONCLUSION

In patients with cN0/pN1 breast cancer treated with BCS and SNB, adjuvant radiotherapy achieved regional control comparable to that observed after ALND, with markedly lower BCRL. Within the SNB group, more extensive radiotherapy fields were not associated with higher BCRL incidence, suggesting that broader nodal coverage may be delivered without substantially increasing lymphedema risk when ALND is omitted.