To better appraise the therapeutic activity of antibodies elicited by ES2B-C001, we studied their inhibitory activity on human HER-2+ breast cancer cells BT-474 (trastuzumab-sensitive) and on the trastuzumab-resistant clone BT-474-C5, growing as three-dimensional (3D) colonies in agar, which represent a better model of tumor architecture than 2D cultures. The gene discussed is ERBB2; the disease is breast cancer.