WNT1 and breast cancer: Given that Cav-1−/− mice could not generate mammary tumors spontaneously, to further investigate the influence of Cav-1 on mice mammary-tumor formation in vivo, MMTV-Wnt1/Cav-1+/− tumor-prone mice were generated by crossbreeding male MMTV-Wnt1 mice with female Cav-1−/− mice (Fig. 4g).