Genetically engineered mouse models (GEMMs) of breast cancer have been proven as a powerful tool for gaining mechanistic insights into tumor initiation, progression, and metastasis as well as for developing innovative cancer therapy.[1] GEMM models for breast cancer commonly use mammary‐gland specific promoters, including MMTV (virus long terminal repeat), WAP (whey acidic protein), and C3 to ensure expression of transgenes in the mammary epithelium. This evidence concerns the gene C3 and breast cancer.