Figure 7 illustrates examples of drug responses within normal CLDN9-expressing cells and CLDN9 knockdown in the breast cancer cell models. Utilizing the cell models established in this study, we validated the responsiveness of these cell lines to chemotherapy agents. As shown in Table 6, knockdown CLDN9 in the Her-2-negative MCF7 and MDA-MB-231 cells sensitized the cells in their response to gemcitabine, docetaxel, methotrexate and, to some degree, cisplatin. However, in the Her-2(+) SKBR3 cells, knockdown CLDN9 only had marginal effects on the cells’ response to these drugs (Table 6). This evidence concerns the gene ERBB2 and breast cancer.