Characteristics and Risk Factors of Axillary Lymph Node Metastasis of Microinvasive Breast Cancer

Abstract Purpose We aimed to select patients who would benefit most from sentinel lymph node biopsy (SLNB) by investigating the characteristics and risk factors of axillary lymph node metastasis (ALNM) of microinvasive breast cancer (MIBC). Methods This retrospective study included 1,688 patients with MIBC who underwent breast surgery with axillary staging at the Asan Medical Center from 1995 to 2020. Results Most patients underwent SLNB alone (83.5%). Seventy (4.1%) patients were node-positive, and the majority had positive lymph nodes < 10 mm, with micrometastasis occurring most frequently (n = 37, 55%). Node-positive patients were more likely to have undergone total mastectomy and axillary lymph node dissection (ALND) compared to node-negative patients (p < 0.001). In the multivariate analysis, independent predictors of ALNM included young age (OR = 0.960; 95% CI: 0.927–0.995; p = 0.023), ALND (OR = 5.285; 95% CI: 2.576–10.842; p < 0.001), more number of harvested lymph nodes (OR = 1.194; 95% CI: 1.119–1.274; p < 0.001), lymphovascular invasion (OR = 8.058; 95% CI: 2.750–23.354; p < 0.001), multiple foci of microinvasion (OR = 2.953; 95% CI: 1.444–6.041; p = 0.003), and hormone receptor positivity (OR = 2.628; 95% CI: 1.293–5.342; p = 0.008). Conclusion A low ALNM rate of 4.1% suggested that routine SLNB for patients with MIBC is unnecessary; however, it can be valuable for selecting patients with specific risk factors. Alongside ongoing trials omitting SLNB in early breast cancer, further sub-analyses focusing on this rare population with MIBC are necessary.