ERBB2 and breast cancer: However, the specificity of trastuzumab PET for HER2 overexpressing breast cancer and the relationship between trastuzumab uptake in-vivo and the immunohistochemistry staining results (which are the accepted standard for treatment with HER-directed therapies) need to be studied further (Ulaner et al., 2016; Ulaner et al., 2017).