Doxycycline administration to MMTV-rtTA;TetO-HER2/neu (MTB;TetO-HER2/neu) and MMTV-rtTA;TetO-Wnt1 (MTB;TetO-Wnt1) mice results in formation of primary mammary adenocarcinomas and, analogous to the treatment of human cancers with targeted therapies, oncogenic pathway inhibition in tumor-bearing mice results in primary tumor regression due to oncogene addiction [17, 19]. The gene discussed is WNT1; the disease is breast adenocarcinoma.