Prognostic impact of HER2-low positivity in patients with HR-positive, HER2-negative, node-positive early breast cancer

Adjuvant therapy for patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, node-positive, early breast cancer (EBC) remains challenging. The prognostic significance of HER2-low positivity in these patients is not fully understood. In our retrospective study, we analyzed 647 patients with HR-positive, HER2-negative, node-positive EBC, stratifying them into three cohorts based on axillary lymph node involvement, tumor size, and characteristics. Cohort 1 included patients with either ≥ 4 positive axillary lymph nodes or 1–3 positive nodes with histological grade 3 or tumor size ≥ 5 cm. Cohort 2 consisted of patients with 1–3 positive nodes, histological grade < 3, tumor size < 5 cm, and Ki-67 ≥ 20%. Cohort 3 comprised patients with 1–3 positive nodes, histological grade < 3, tumor size < 5 cm, and Ki-67 < 20%. We compared invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) between HER2-low (IHC1+ or IHC2+/FISH−) and HER2-zero (IHC0) groups in each cohort. In cohort 1, HER2-low patients exhibited significantly better 5-year IDFS (84.2% vs. 73.6%, p = 0.0213) and DRFS (88.2% vs. 79.8%, p = 0.0154). However, no significant differences were observed in cohorts 2 and 3. Our findings suggest HER2-low positivity as a prognostic factor in HR-positive, HER2-negative, and node-positive EBC.