For example, overexpression and activating mutations of genes encoding members of the ErbB receptor family (for example, EGFR or ErbB1 in non-small-cell lung cancer and colorectal cancer, and ErbB2, also called HER2, in breast cancer) are used to identify subgroups of tumors responsive to small molecule agents (e.g., gefitinib, erlotinib) or monoclonal antibodies (e.g., cetuximab, trastuzumab) that specifically target ErbB receptors [65,66,67]. Here, ERBB2 is linked to breast cancer.