ERBB2 and neoplasm: The targeting ligands can identify a variety of representative tumor biomarkers, such as FR, TfR, insulin receptor (IR), estrogen receptor α (ERα), prostate-specific membrane antigen (PSMA), mucin-1 (MUC1), nucleolin, and human epidermal growth factor receptor 2 (HER2) [10,11,29,30,31].