Taken together, the MD allele intervenes with tumorigenesis at multiple stages, but in a transgene-specific manner, namely most prominently in the MMTV-PyVT mouse model for human luminal breast cancer and MMTV-neu mouse model for human HER2+ luminal breast cancer, but less prominently in the C3(1)-TAg mouse model for human basal breast cancer. The gene discussed is ERBB2; the disease is breast carcinoma.