Abstract
PURPOSE: Human epidermal growth factor receptor 2 (HER2)-low breast cancer has been recognized as a distinct biological subset within HER2-negative breast cancer. This study aimed to examine the differences in sentinel lymph node metastasis (SLNM) rates and prognosis between HER2-low and HER2-zero breast cancers. METHODS: This retrospective study evaluated 965 estrogen receptor-positive, HER2-negative breast cancer patients who underwent sentinel lymph node biopsy at Osaka Metropolitan University Hospital. Clinicopathological characteristics, SLNM rates, and prognostic outcomes were compared between patients with HER2-low and with HER2-zero breast cancers. RESULTS: The SLNM rate was significantly higher in the HER2-low group than in the HER2-zero group (p = 0.039). However, disease-free survival (DFS), recurrence-free interval (RFI), overall survival, and breast cancer-specific survival were not significantly different between the two groups. In subgroup analysis excluding macrometastases, DFS and RFI were significantly longer in the HER2-low breast cancer group. CONCLUSION: HER2-low breast cancer exhibits a higher SLNM rate, suggesting unique biological behavior. However, its overall prognosis remains similar to that of HER2-zero breast cancer, with potential prognostic advantages in select subgroups.