Excluding upper axillary level 1 in regional nodal irradiation does not increase axillary recurrence risk in patients with breast cancer.

Abstract

Purpose: The optimal extent of regional nodal irradiation (RNI) in postoperative radiotherapy for breast cancer, particularly regarding axillary level 1 (AXL1), remains uncertain. This study aims to compare clinical outcomes between extensive RNI including the entire axilla and limited RNI excluding the upper AXL1 in patients with breast cancer.

Methods: A retrospective analysis included 1,780 women with non-metastatic unilateral breast cancer who underwent RNI during postoperative radiotherapy between 2007 and 2018. Patients were classified into extensive and limited RNI groups based on the upper AXL1 inclusion in the radiation field. Propensity score matching yielded a cohort of 1,020 patients. Non-inferiority of limited RNI compared to extensive RNI was assessed with a defined margin of ≤2% in the 5-year axillary recurrence rate.

Results: After a median follow-up of 67.9 months, the 5-year axillary recurrence rates were similar between extensive and limited RNI groups (1.2% vs. 1.6%; P_log-rank=0.790). Limited RNI demonstrated non-inferiority with a 0.4% difference (95% confidence interval, -1.1%-1.9%; P_{non-inferiority}=0.019). Disease-free survival (87.9% vs. 91.5%; P_log-rank=0.122) and overall survival (94.1% vs. 96.9%; P_log-rank=0.260) at 5 years were not significantly different between extensive and limited RNI groups. Multivariable analysis revealed that lymphovascular invasion (hazard ratio [HR], 5.17; P=0.02) and negative hormone receptor status (HR, 11.73; P=0.002) were associated with a higher risk of axillary recurrence, while limited RNI showed no significant association (HR, 1.35; P=0.652). Subgroup analysis demonstrated that extensive RNI did not improve axillary control in patients with lymphovascular invasion, hormone receptor negativity, positive lymph node metastasis, or a small number of nodes removed.

Conclusion: Limited RNI, excluding the upper AXL1 from the radiation field, demonstrated axillary recurrence rates comparable to those of extensive RNI in patients with breast cancer. The study suggests that extensive RNI may not provide additional therapeutic benefits, while limited RNI appears to be a valid option for regional control.