In order to confirm the role of MTDH in the sensitivity of breast cancer cells to doxorubicin, we designed three different short-hairpin RNA constructs (MTDH-siRNA1, MTDH-siRNA2, and MTDH-siRNA3) to knock down MTDH in MCF-7/ADR cell line. The gene discussed is MTDH; the disease is breast cancer.