Incidence and Prognostic Values in Human Epidermal Growth Factor Receptor 2-Low Expression Metastatic Breast Cancer in Southeast Asian Population: A 10-Year Retrospective Study

Abstract

PURPOSE Breast cancer progression varies across molecular subtypes, and treatment options for human epidermal growth factor receptor 2 (HER2)-low expression tumors are limited compared with those of HER2 overexpression tumors. Comprehensive information regarding the epidemiology and clinical outcomes of metastatic HER2-low expression breast cancer in a Southeast Asian population is lacking. METHODS This retrospective cohort study was performed to analyze data from patients with de novo advanced breast cancer, including HER2 expression, tumor stage, and metastatic pattern. Statistical analyses, including chi-square tests and survival analyses, were used to compare HER2-low expression and HER2-negative groups. RESULTS Of the 491 patients, 21.2% had HER2-low expression, 30% had HER2 overexpression, and 50% had HER2-negative expression. Among the hormone receptor (HR)–positive patients, 34% had HER2-low expression; in the triple-negative patients, the HER2-low incidence was 20.6%. No significant differences in clinical characteristics between HER2-low and HER2-negative groups were observed, except for more HR-positive patients in the HER2-low group. HER2-low patients had a longer overall survival (OS) than HER2-negative patients (43 v 23 months; hazard ratio, 0.7; P < .001), especially in HR-positive patients. After adjusting for HR status, HER2-low patients maintained improved outcomes. HR-positive HER2-low patients showed nonsignificant OS gains compared with HR-positive HER2-negative patients, regardless of first-line chemotherapy or endocrine therapy. CONCLUSION This study revealed the incidence and clinical outcomes of HER2-low expression in de novo advanced breast cancer, suggesting favorable outcomes, particularly in HR-positive breast cancer. These findings may inform personalized treatment strategies. Further research into the mechanisms and implications of HER2-low expression in breast cancer is required.