ERBB2 and cancer: The antibody fragment strategy allowed the targeting of various cancer associated proteins such as CD38, epidermal growth factor receptor 1 [113,114], folate receptor 1 [109], prostate specific membrane antigen [110], human epidermal growth factor receptor 2 (HER2/neu) [77], prominin or CD133 [115,116], and plasminogen activator urokinase receptor [117,118].