ERBB2 and breast cancer: HER2 is overexpressed in 30% of invasive breast cancers.15 Trastuzumab inhibits receptor dimerization and internalization, leading to endocytic destruction of the receptor and immune activation.15 Other targets besides growth factors include hematopoietic differentiation antigens (CD20, CD30, CD33, CD52), which are glycoproteins found on the surface of normal and tumor cells.19 For instance, rituximab (Rituxan), a mAb used for lymphoproliferative disorders, targets CD20, a pan B‐cell marker,20 leading to the interactions between FcγR expressed on immune cells and the Fc region of the mAb.