HER2-TTC demonstrated potent in vitro cytotoxicity in various HER2-positive cancer cell lines and strong in vivo antitumor efficacy both in subcutaneous KPL-4 and Calu-3 xenograft models and in an intratibial BT-474 mouse model mimicking breast-cancer-induced metastatic bone disease. The gene discussed is ERBB2; the disease is breast carcinoma.