The role of adjuvant endocrine treatment in ER+, PR-, HER2-early breast cancer: a retrospective study of real-world data

Purpose: Estrogen receptor-positive (ER+), progesterone receptor-negative (PR-) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer (BC) often developed resistance to endocrine treatment (ET). We aimed to explore (1) the different clinicopathological features between ER+/PR+/HER2- and ER+/PR-/HER2- BC, and (2) whether ER+/PR-/HER2- early BC patients could benefit from adjuvant ET. Methods: All patients treated for ER+/HER2- early BC who underwent surgery between 2010 and 2021 from a BC database in China were retrospectively examined. The cases followed up for less than six months were excluded. Results: The records of ER+/PR+/HER2- (n = 10843) and ER+/PR-/HER2- BC (n = 1193) cases were reviewed, with median follow-up times of 35.8 and 47.0 months, respectively. Compared with ER+/PR+/HER2- cases, ER+/PR-/HER2- BC occurred more in postmenopausal women (73.1% vs. 52.9%, p = 0.000) and were more likely to be T > 2 cm (40.6% vs. 37.6%, p = 0.048) and Ki67 > 20%+ (48.1% vs. 36.9%, p = 0.000). However, ER+/PR-/HER2- cases had fewer nodal involvement (32.9% vs. 36.9%, p = 0.000). Approximately 82.2% (981/1193) of ER+/PR-/HER2- patients received ET, while approximately 17.8% (212/1193) did not. Compared to patients did not receive adjuvant ET, the ET group had similar disease-free survival (DFS) (HR = 1.33, 95% confidence interval (CI): 0.68-2.59, p = 0.444) and overall survival (OS) (HR = 1.17, 95%CI: 0.37-3.68, p = 0.799). 65.7% of recurrent ER+/PR-/HER2- patients experienced distant relapse (65.7% vs. 48.2% (for ER+/PR + cases), p = 0.011). By comparison, recurrent ER+/PR+/HER2- patients were more likely to experience only local relapse (31.6% vs. 14.9% (for ER+/PR- cases), p = 0.007). Conclusions: ER+/PR-/HER2- BC was a special subtype with aggressive clinicopathological features and more tend to have distant metastasis rather than nodal involvement or local relapse. ER+/PR-/HER2- early BC did not seem to benefit from adjuvant ET.