To determine whether adaptive immunity is required for sustained regression of mammary adenocarcinomas, we injected limited passage tumor cells derived from primary mammary tumors arising in MTB;TetO-HER2/neu (HER2/neu-Prim1) or MTB;TetO-Wnt1 (Wnt1-Prim1) mice into the mammary fat pads of immunocompromised female nu/nu mice maintained on doxycycline. This evidence concerns the gene ERBB2 and breast cancer.