MMTV-rtTA;TetO-PTHrP; MMTV-PyMT; MMTV-Cre;PTH1Rlox/lox (Tet-PTHrP;PyMT;Cre;PTH1RLox) mice on Dox were followed for the development of mammary tumors and compared to Tet-PTHrP;PyMT;PTH1RLox mice that lacked the Cre transgene. This evidence concerns the gene PTHLH and breast cancer.