CD4 and neoplasm: They act as antigen-presenting cells to CD4+ T cells, which are crucial for trastuzumab activity.24 The similar modulation of the LCK and HCK metagenes, reflecting the infiltration of T cells and monocytes,13 indicates that trastuzumab is active in tumours in which the entire immune system cycle is stimulated or inducible by trastuzumab.