ERBB2 and neoplasm: Moreover, a trastuzumab concentration-dependent attenuation of target cancer cell HER2 expression (although direct HER2 internalization by trastuzumab is one possible mechanism of down-modulation of HER2), and reciprocal increase in CD14+ and CD56+ immune cell HER2 expression, was observed in the HER2+ patient tumor cell–autologous PBMC trogocytosis assay (Additional file 3: Figure S3A).