Omitting axillary dissection in patients with 1-2 sentinel node–positive breast cancer undergoing mastectomy in China: A retrospective cohort study with target trial emulation.

e12577 Background: Trials have demonstrated the safety of omitting axillary dissection in patients with cT1-3, cN0, or iN0 breast cancer, and 1-2 sentinel-node involvement, who underwent breast-conserving surgery (BCS). Given the limited data on mastectomy patients in similar studies in China, and the uncertain impact of radiotherapy on these outcomes, we aim to investigate whether omitting axillary dissection is non-inferior to performing it in patients with one or more macrometastatic sentinel nodes undergoing mastectomy in China. Methods: We retrospectively emulated a target multicenter, non-blinded, noninferiority trial to assess the sentinel-lymph-node biopsy only (SLNB only) with completion axillary-lymph-node dissection (ALND) in patients undergoing mastectomy from medical database between 2014 and 2022, and prospectively conducted a randomized, noninferiority trial between 2022 and 2024. Patients were eligible if they had clinically node-negative primary T1-3 breast cancer, with 1-2 sentinel-node macrometastases. Adjuvant treatment and radiation therapy were used in accordance with national guidelines. The primary endpoint was recurrence-free survival (RFS), and the second endpoint was overall survival (OS). Non-inferiority was defined as the hazard ratio (HR) of less than 1.46 for no axillary dissection versus axillary dissection. This trial was registered with Chictr.org.cn , ChiCTR2300072140. Results: A total of 1,090 eligible patients were enrolled across seven centers. Of these, 438 patients (40.2%) were assigned to the SLNB-only group, and 652 patients (59.8%) were assigned to the ALND group. After a median follow-up of 44.7 months, 79 patients experienced recurrence or death. The estimated 5-year recurrence-free survival rate was 89.8% (95% confidence interval [CI], 85.6%–94.2%) in the SLNB-only group and 90.8% (95% CI, 88.2%–93.6%) in the ALND group, with a hazard ratio for recurrence or death of 0.91 (95% CI, 0.57–1.45). This result was significantly below the pre-specified non-inferiority margin (P < 0.001). The primary analysis remained consistent across key subgroups and sensitivity analyses. The hazard ratio for recurrence or death in the SLNB only group as compared with ALND group included 1.00 in all subgroups. Radiotherapy (78.5% vs. 58.7%) and chemotherapy (96% vs. 93.2%) were administered more frequently in the ALND group compared to the SLNB-only group. Conclusions: In patients with clinically node-negative invasive breast cancer and 1–2 sentinel-lymph-node macrometastases, omission of axillary dissection was non-inferior to axillary dissection in terms of recurrence-free survival. Clinical trial information: ChiCTR2300072140 .