ERBB2 and cancer: Second, the selection of most appropriate TAT molecules will also depend on the targeting antigen and it expression frequency, density, specificity and location (e.g. Prostate specific membrane antigen - PSMA, human epidermal growth factor receptor 2, c-erbB2 - HER2/neu, mesotelin –MSLN, B-lymphocyte antigen CD20) proposing the opportunity to adapt the features of the TAT agent to a particular type of cancer.