Evaluation of breast cancer subgroups with different HER2 expression levels based on 18F-FDG PET/CT characteristics

Purpose HER2-low expression breast cancer (BC) is an emerging concept. However, the clinical and molecular markers thereof are unknown. The purpose of this study was to explore the differences among those subgroups with differential HER2 expression. Methods Data were collected from 248 patients with BC who underwent PET/CT imaging scan, including clinicopathological characteristics, PET/CT parameters, and 2-year progression-free survival (PFS). Based on HER2 expression levels, all patients were divided into three subgroups: patients with HER2-zero, HER2-low, and HER2-over expression. Data were analyzed and compared among the three subgroups. The Mann-Whitney U test, chi-square test, and Student’s t-test were performed for statistical analysis. Results Patients with HER2-low expression had a higher hormone receptor (HR)-positivity rate (79.9% vs. 51.5% (HER2-zero) and 58.0% (HER2-over expression), P < 0.001). The HER2-low group had a significantly lower Ki-67 expression rate than that of the HER2-zero group ( P = 0.005). When comparing the metabolic tumor volume (MTV) and total lesion glycolysis (TLG), significant differences were found between the HER2-low and HER2-over expression groups ( P = 0.029 and P = 0.018, respectively). Compared to HER2-zero expression tumors, a statistically lower SUVmax was detected in HER2-low expression tumors ( P = 0.034). The 2-year PFS rate in the HER2-low group was 73.9%, which was higher than that in the HER2-zero group (63.6%) and lower than that in the HER2-overexpression group (88.9%) ( P = 0.006). Conclusion The clinicopathological characteristics, PET/CT features, and survival outcomes in patients with HER2-low expression differed from those in patients with HER2-zero and HER2-over expression, suggesting the need for precise clinical therapy.