Role of MDM2 Overexpression in Doxorubicin Resistance of Breast Carcinoma

Several oncoproteins or tumor suppressor gene products have been indicated to be of value as predictors of the de novo resistance to cytotoxic agents. In this study, we have investigated the role of MDM2 (murine double minutes) overexpression in doxorubicin resistance of breast cancer. Immunocytochemical analysis demonstrated that MDM2‐positive tumors, even with p53‐negative pheno‐type, were significantly more resistant to doxorubicin treatment compared to MDM2‐negative tumors. An in vitro experimental model using stable mdm2‐transfected MCF‐7 cells carrying wild‐type p53 confirmed that the cells become approximately 3‐fold more resistant to doxorubicin as a result of MDM2 overexpression, and the wild‐type p53 function, such as the induction of p21(Waf1) following DNA damage, was significantly suppressed. MDM2 overexpression is suggested to be a novel marker for predicting lack of response to doxorubicin treatment in breast cancer patients.