Mouse xenograft tumor model

All animal procedures and care were conducted in accordance with the animal care and use guidelines and the protocol was approved by the Animal Welfare Committee (AWC) of the University of Texas Medical School at Houston. Breast cancer cells (BT474) with high HER2 expression were prepared and implanted into athymic nude mice (Foxn1^nu/Fox1⁺ genotype, Envigo, East Millstone, NJ, USA) subcutaneously (sc.) at the hind-leg fat pad to establish tumors as we described previously [7]. BT474 breast cancer cells (5 × 10⁶ cells/mouse) were implanted into 6 to 8 week old mice and antibody treatment was initiated after one additional week. The mAb treatments were performed once a week by intraperitoneal (ip) injection for 5 weeks at a dosage of 10 mg/kg body weight. Tumor growth and mouse health were monitored twice per week. Tumor growth was quantified by measuring the size of tumors using a Vernier scale caliper.