El carcinoma mioepitelial (CM) es una neoplasia maligna rara que se origina en células mioepiteliales, presentes en diversas glándulas, incluyendo la mamaria. Su presentación clínica es inespecífica, manifestándose como una masa de crecimiento rápido. En este caso, se reporta una paciente de 80 años con dolor mamario, masa palpable y telorrea sanguinolenta. La biopsia confirmó un carcinoma mioepitelial originado en un adenomioepitelioma (AM) con un componente invasivo de 3 mm. Se realizó cuadrantectomía central con márgenes negativos y biopsia de ganglio centinela negativa. Recibió radioterapia adyuvante y, debido a las características histológicas, se decidió no administrar terapia sistémica adicional. Este caso destaca la importancia de incluir el AM en el diagnóstico diferencial de lesiones mamarias en mujeres posmenopáusicas y resalta el papel de la inmunohistoquímica en su diagnóstico. La paciente se encuentra en seguimiento semestral sin evidencia de recurrencia hasta el momento.

Background/Objectives: 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. Methods: 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). Results: 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. Conclusions: 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.