The mechanism of action of mAbs was previously thought to involve blocking the physiological function of the target (e.g. a growth factor or cytokine receptor) by the Fab portion but recent studies have demonstrated stimulation of the immune system by the Fc portion; Fc gamma receptor-mediated activation of macrophages and natural killer cells leading to ADCC is necessary for the anti-tumor effects of Rituximab (anti-CD20) and Trastuzumab/Herceptin (anti-Her2/ErbB2)7. The gene discussed is ERBB2; the disease is neoplasm.