Abstract: Background and purpose: Neoadjuvant chemotherapy (NAC) has become the standard treatment mode for locally advanced breast cancer patients. This study aimed to evaluate the clinical benefits of internal mammary sentinel lymph node biopsy (IMSLNB) in patients with breast cancer who underwent NAC. Methods: From Apr. 2014 to Apr. 2018, 202 patients with primary breast cancer who underwent operation after NAC were included in this study. All patients received radiotracer injection with modified injection technology. IMSLNB was performed on patients with internal mammary sentinel lymph node (IMSLN) visualization. Results: Among the 202 patients, the visualization rate of IMSLN was 34.2% (69/202), and it was 11.6% (8/69) and 88.4% (61/69) among patients with clinical node-negative and clinical lymph node-positive (cN⁺) disease, respectively. Furthermore, the success rate of IMSLNB was 98.6% (68/69). The detection rate of IMSLN was 33.7% (68/202), and the metastasis rate was 11.8% (8/68). One of the 8 patients with IMSLN metastasis was not associated with axillary lymph node (ALN) metastasis (N₀ to N_1b), 2 patients with 1-3 ALN metastases (N_1a to N_1c), 4 patients with 4-9 ALN metastases (N_2a to N_3b), 1 case with ≥10 ALN metastases (N_3a to N_3b), and the postoperative pathological stage also changed (0 stage to ⅠB stage, ⅡA/ⅢA stage to ⅢC stage). These 8 cases of IMSLN metastases received internal mammary node irradiation (IMNI) after operation. Conclusion: Patients with visualization of IMSLN should receive IMSLNB after NAC, especially for patients with cN⁺ disease, in order to complete lymph nodal staging. IMSLNB could further improve the definition of nodal pathologic complete response and guide the IMNI.

Key words: Breast cancer, Neoadjuvant chemotherapy, Internal mammary sentinel lymph node biopsy, Modified injection technology