ERBB2 and breast carcinoma: It is of interest to note that four of the most widely used MAbs in cancer therapy are of this IgG1 isotype: cetuximab targeting the EGF-R in colorectal, head and neck, and lung carcinomas, rituximab targeting CD20 in lymphoma, and trastuzumab and pertuzumab targeting HER2/neu in breast carcinoma.