Clinical significance of HER2 status in T1bN0 breast cancer: a nationwide study from the Korean Breast Cancer Society

Purpose The prognosis of patients with node-negative T1b tumors according to human epidermal growth factor receptor 2 (HER2) status is not known. This group of patients has not been studied in the available randomized trials. The objective of this study was to evaluate the survival of patients in a monoethnic group diagnosed with T1b lymph node-negative breast cancer depending on HER2 status. Methods We analyzed 3110 patients with T1bN0M0 breast cancer whose data were deposited into the Korean Breast Cancer Society Registry database between 2000 and 2009. Overall survival (OS) and breast cancer-specific survival (BCSS) were compared according to HER2 status. Results Among all patients, 494 (15.9%) had HER2-positive breast cancer. At a mean follow-up of 93 months, 108 deaths and 86 breast cancer-specific deaths were noted among all patients. There was no significant difference in OS between the HER2-negative and HER2-positive groups (p = 0.103). The same result was observed for BCSS. However, in the subgroup of estrogen receptor (ER)-positive women, HER2-negative patients had a better BCSS prognosis than HER2-positive patients (p = 0.025). Multivariate analysis also indicated a significant difference in BCSS in the ER-positive subgroup (HR 2.60; 95% CI 1.15-5.87; p = 0.021). Conclusion This study analyzed a large nationwide and monoethnic cohort and found a significant difference only in BCSS in the ER-positive subgroup according to HER2 status. Anti-HER2 therapy may be considered in HER2-positive and ER-positive patients with small, node-negative breast cancer.