Two xenograft tumor models overexpressing HER2, BT-474 (human breast cancer cells), and NCI-N87 (human gastric cancer cells), were used to compare the effects of ABP 980 and trastuzumab to demonstrate that ABP 980 has a similar ability to inhibit tumor growth in vivo as well as in vitro. The gene discussed is ERBB2; the disease is breast carcinoma.