As distant recurrence is the principal cause of mortality from breast cancer, we examined micrometastatic disease in the lung following oncogenic pathway inhibition in MTB;TetO-HER2/neu;TetO-TurboCre;Rosa26-lox-stop-lox-YFP (MTB;TetO-HER2/neu;TTC;rYFP) mice. This evidence concerns the gene ERBB2 and breast cancer.