More than 25 different murine GEMMs for breast cancer expressing different genes/oncogenes such as, PyMT (polyoma middle T antigen), SV40 T antigen, ErbB2/Neu, cyclinD1, Ras, Myc, TGF‐α, and Wnt1 have been established.[2] The most widely used models are MMTV‐Neu and MMTV‐PyMT, which result in the development of multifocal adenocarcinoma and metastatic lesions in the lungs and/or lymph nodes. The gene discussed is ERBB2; the disease is adenocarcinoma.