Oncological Outcomes of De-Escalation of Axillary Surgery in Breast Cancer Patients at a Referral Cancer Center in Colombia

<b>Background/Objectives</b>: De-escalation of axillary surgery with sentinel lymph node biopsy (SLNB) has been shown to decrease morbidity in breast cancer patients without affecting oncological outcomes. However, there are very few reports on its applicability in real-world clinical practice, especially in middle-income countries. <b>Methods</b>: A retrospective historical cohort study was conducted, including 787 patients with clinical stage I-IIIA breast cancer treated from 2013 to 2023 at the INC in Colombia. Two groups were analyzed based on the timing of the axillary procedure: patients undergoing SLNB as initial surgery (Upfront SLNB) and those receiving neoadjuvant chemotherapy (Post-NACT SLNB). <b>Results</b>: The overall sentinel lymph node (SLN) identification rate was 99.3%. SLN positivity was 32% in Upfront SLNB and 13.1% in Post-NACT SLNB. Axillary lymph node dissection (ALND) was omitted in 56% of patients with node-positive Upfront SLNB; it was avoided in 86.8% of the Post-NACT group with complete axillary response (ypN0). Regional recurrence rates were 2.33%. In multivariate analysis, the main factors linked to recurrence and mortality were triple-negative and luminal B HER2-negative biological subtypes, histological grade 2, and tumor size ≥ 2 cm. At 60 months of follow-up, 91.4% (95% CI: 88.9-93.9) of patients remained recurrence-free (time-recurrence (TR)), and overall survival (OS) was 96.1% (95% CI: 94.5-97.7), with no differences observed based on the axillary surgical strategy. <b>Conclusions</b>: Sentinel lymph node biopsy (SLNB) is an oncologically safe procedure for patients with early-stage and locally advanced breast cancer with an adequate response to neoadjuvant systemic treatment.