Cetuximab (C225) is a monoclonal antibody that inhibits epidermal growth factor receptor (EGFR), with a Kd of 0.201 nM for soluble EGFR by SPR. Cetuximab also exhibits a Kd of 0.147 nM for EGFR in fixed A431 cells by ELISA. Cetuximab (C225; 30 nM) time-dependently inhibits the proliferation of SCC-1, SCC-11B, SCC-38, and SCC-13Y cells after treatment for 8 d. Cetuximab (30 nM) causes G0/G1 arrest, induces apoptosis, and reduces Rb, p27, Bcl-2, and Bax expression in SCC-13Y cells. Cetuximab (30 nM) also enhances radiosensitivity and increases radiation-induced apoptosis in SCC-13Y cells.