The authors concluded that increasing the specific activity by conjugation of MCPs to trastuzumab greatly amplified the cytotoxic potency against HER2-overexpressed breast cancer cells and extended its cytotoxicity to cells with intermediate HER2 expression but without gene amplification, as well as to cells that are HER2 overexpressed but trastuzumab-resistant. Here, ERBB2 is linked to breast cancer.