SMAD4 and breast cancer: For example, Wap-Cre driven mutation of Smad4 and Brca2 causes a very high frequency of affected mice to develop mammary tumors (100% and 77%, respectively), whereas only 15% of mice with Wap-Cre driven mutation of Brca1 develop mammary tumors and no tumors are obtained following Wap-Cre driven mutation of Pparγ or Stat3[43]–[47].