ERBB2 and breast cancer: To address whether mice bearing fully regressed mammary tumors harbor dormant residual disease, we re-administered doxycycline to intact MTB;TetO-HER2/neu mice whose primary tumors had regressed to a non-palpable state following doxycycline withdrawal, but had not exhibited spontaneous tumor recurrences when maintained off doxycycline for a period of 6 months.